Call

High-performance timing detector for the HL-LHC Upgrade of the CMS experiment at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 144 - Joao Varela

Co-Supervisor: 1704 - Tahereh Niknejad

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program: Engineering Physics

Typology: National

In the High-Luminosity phase of the LHC physics program, the accelerator will provide an additional integrated luminosity of 3000 fb-1. One of the main challenges that must be overcome is the very high pileup (PU) originated by the high luminosity. Each of the colliding beams at the LHC consists of many intense bunches of protons. At the HL-LHC, the average number of interactions in a single bunch crossing is 200 (named ‘pileup interactions’). Most of these interactions are not interesting in the searches for New Physics at the TeV scale. They contain low transverse momentum (pT) particles and deposit little energy in the CMS detector. A relatively small fraction of all interactions are hard collisions producing particles with high pT. Nevertheless, the presence of tracks and energy from 200 extra collisions degrades the reconstruction of the hard scatter. Pileup produces many hits in the tracking detectors, leading to mismeasured or misidentified tracks. It also adds extra energy to the calorimeter measurements, such as jet energies, associated with the hard scatter collision. Electroweak phenomena, which are of special interest, are often characterized by having isolated leptons. Energy or tracks from pileup can contribute to an activity that is not due to the collision containing the leptons or photons and cause them to appear as non-isolated. In general, pileup confuses the reconstruction and interpretation of events. The development of a new Timing Detector to be integrated in the CMS experiment aims at fighting the pileup background, substantially improving the sensitivity to New Physics. In the time domain, pileup collisions at the HL-LHC will occur with an r.m.s spread of approximately 180 ps within the bunch crossing structure of the colliding beams. Slicing the beam spot in consecutive time exposures of 30 ps allows to reduce the number of vertices per exposure to about 30. A time resolution of this order would, therefore, reduce the effective multiplicity of concurrent collisions to a level comparable to the present LHC. However, the required time resolution is one order of magnitude better than achieved in the current CMS detector. The Timing Detector (MTD) is a dedicated timing layer in front of the calorimeters capable to measure the time of charged particles with a precision of 30 ps. The subject of the PhD thesis is the development of a new timing technology based on state-of-art LYSO scintillating crystals, associated to silicon-photomultipliers and Application Specific Integrated Circuits (ASICs) developed at LIP in collaboration with Portuguese industry. The thesis work will be done in the context of a collaboration with several institutes in Europe and in the US. The LIP-CMS group is fully responsible for the design and construction of the readout system of the 330’000 sensors composing the Barrel Timing Layer, benefiting from a long experience in the development and leadership of large instrumentation projects. The development and test of prototypes is carried in the TagusLIP laboratory at Taguspark, Oeiras. Stays at CERN to perform tests and measurements with dedicated proton beams at the SPS will be required. Visits to other research facilities to perform tests of resistance to radiation of the prototypes detectors and electronics are also foreseen. The research will be carried in the frame of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”.

Probing the limits of the Standard Model with forward proton tagging at ATLAS

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 55 - Patricia Conde Muino

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: PhD in Physics

Typology: National

The non-abelian structure of the gauge theory in the SM implies the existence of triple and quartic gauge boson couplings (TGC and QGC, respectively) fully constrained by the gauge symmetry. The measurement QGC provide a window into the Electroweak symmetry breaking mechanism, given the fact that the longitudinal modes of the W and Z bosons are Goldstone bosons. Deviations from the SM predictions can appear due to interchange of new particles, integrated out in the effective interaction, in new physics theories. Models with a new heavy scalar singlet interacting with the Higgs sector can modify the quartic gauge boson couplings but not the triple ones. It is, therefore, essential to probe this missing part of the SM, measuring both the TGC and QGC. 
  The ATLAS sensitivity to anomalous couplings in the γγWW, γγγγ and γγZZ vertices can be improved two orders of magnitude by using the ATLAS Forward Proton tagging detectors (AFP) [1]. AFP effectively converts the LHC into a photon-photon collider: the two scattered protons emit two photons that annihilate to produce a pair of vector bosons (two W’s, for instance). The protons, that stay intact after the interaction, are scattered through very small angles and they are detected at the AFP stations. Since there is no underlying event, the two vector bosons are the only particles produced centrally. If they decay to leptons they can be easily triggered and identified. The invariant mass of the vector boson pair can be measured precisely by determining the proton energy loss with the AFP detectors, even in the case of neutrinos in the final state. The presence of anomalous quartic gauge boson couplings could be observed as an increase in the number of detected vector boson pairs with large invariant masses. This project proposes the search for anomalous couplings of the type γγWW using the AFP detectors. The work plan requires participating in data taking preparations and the AFP detector performance studies, fundamental to obtain the best possible proton tagging performance and, hence, the best possible sensibility to anomalous couplings. The analysis will start with the already collected Run-2 data and will later continue with the available Run-3 data (data taking starting this year!). The work will be developed in an international environment, in collaboration with experts from other European institutions. Frequent presentations of the results achieved are expected, either in collaboration meetings at CERN or by videoconference. References [1] E. Chapon, C. Royon, and O. Kepka, Anomalous quartic WWγγ, ZZγγ, and trilinear WWγ couplings in two-photon processes at high luminosity at the LHC, Phys.Rev. D81 (2010) 074003, arXiv:0912.5161 [hep-ph]. 


RPCs in Astroparticle and their associated technologies

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 6 - Pedro Assis

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program: Eng. Física Tecnológica

Typology: National

The LIP group participating in the Pierre Auger Observatory has been developing the Resistive Plate Chamber technology to be used in the context of Astroparticle Physics experiments. These are normally composed of distributed stations at remote locations and have stringent requirements on power, communications and price. Currently the RPCs developed have been working with no problems in the Pierre Auger Observatory site located in the Pampa Argentina at 1400 m of altitude. The solution developed has a good timing resolution of the order of the few ns (limited by the electronics and clock synchronization) but present a modest spatial resolution of the order of tens of cm. This resolution derives from the readout panel used composed of a matrix of pads with this size. In applications for the future detectors or for the detailed study of detectors response it is desirable to reach, at least, resolution of the order of the cm that allows to achieve angular resolutions better than the degree . The simplest way of increasing the resolution is to maintain the readout paradigm and simply reduce the pad size. However this would lead to a growth of the number of acquisition channels with the number of pads to the square. The aim of this thesis is to explore and develop solutions in which the increase on the resolution grows, at most, linearly with the factor gained in resolution. Changes can be considered at the detector level but solution will be investigated in the changing of the readout paradigm and on the instrumentation of the detector.

Signatures of gravitational waves in non-homogeneous cosmologies

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 226 - Antonio da Silva

Co-Supervisor: 1861 - Alberto Krone-Martins

Co-Supervisor: 111 - José Pedro Mimoso

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astronomy Astrophysics - FCUL

Typology: Mixed

Abroad-Institution: University of California, Irvine, Donald Bren School of Information and Computer Sciences, Department of Informatics, USA

So far, gravitational waves have been described in the context of homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) models. A more general class of non-homogeneous Lemaitre-Tolman-Bondi (LTB) models may be a more natural and an observationally consistent alternative to the present homogeneous and isotropic paradigm. Predictions for gravitational waves from the early universe and from astrophysical sources are still missing for this class of models and are necessary for the preparation of the next ESA flagship missions for cosmology: LISA and Euclid. The main objective of this project is to develop the framework of GW generation in LTB, and build realistic simulations of the GW background based on it, using a combination of N-body and Machine Learning methodologies. The plan is to perform and detailed characterization of the properties of the GW signal that will be detected by future GW experiments for this class of models. We will also propose to explore the complementarity between GW and other (wavelength) surveys, using a multi-messenger approach, to identify cosmological signatures of LTB non-homogeneity in future datasets.

Probing the primordial quark gluon plasma with heavy flavour

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Co-Supervisor: 1788 - Yen-Jie Lee

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Ph.D in Physics at IST (Doutoramento em Física no IST)

Typology: National

At the LHC we recreate droplets of the primordial medium that permeated the universe in its first microseconds. This hot, dense, coloured medium, the quark-gluon plasma (QGP), is produced in ultra-relativistic heavy-ion collisions. The highest energies attained at the LHC and its state-of-the-art detectors are facilitating tremendous advancements in our understanding of the strong interaction, and of QCD matter at extreme conditions. Such data-driven advances also highlight unexpected behaviour, and the study of the QGP medium is fostered by novel probes facilitated by the large datasets being collected. One such probe is provided by heavy quarks. The bottom quarks are particularly interesting probes, as they are produced early in the collision and thus experience the full evolution of the hot medium. The aim of the Thesis project is the detection and study of b-quark hadrons in heavy-ion collisions (with particular the focus on the still-to-be-detected B0 meson, the rarer Bc meson, and possible exotic hadrons). These novel probes facilitate unique information on the flavour and mass dependence of energy loss mechanisms, as particles traverse the medium, and on underlying quark-recombination mechanisms yet to be observed at these scales. The Thesis project aims at making unique contributions to further our understanding of the primordial medium, by exploring novel probes and unprecedented energies at the LHC.

Rare Higgs decays and couplings to quarks

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Co-Supervisor: 1777 - Sandro Fonseca de Souza

Co-Supervisor: 1780 - Eliza Melo da Costa

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Ph.D in Physics at IST (Doutoramento em Física no IST)

Typology: National

Since the discovery of the Higgs boson at the LHC in 2012, by the CMS and ATLAS experiments, the focus has been placed in measuring its properties. In particular, on the determination of how it couples to the other Standard Model (SM) particles. In the last few years, both CMS and ATLAS have detected the couplings of the Higgs to the heaviest quarks: the top (ttH) and the bottom (H->bb). The next big, and natural, step in this endeavour is to access the H couplings to the lighter quarks. The thesis project consists in the search for Higgs boson decays to a quarkonium state and a photon, using the large dataset collected by CMS at the LHC. The motivation for the study is to experimentally constrain the Higgs-quark couplings, and help decide whether our new boson is indeed the particle at the core of the SM, or (even more excitingly) a first particle beyond the SM.

Coding the Cosmos: Simulating Superstrings in the GPU Era

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program: MAP-fis

Typology: National

Cosmic strings arise naturally in many proposed theories of new physics beyond the standard model unifying the electroweak and strong interactions, as well as in many superstring inspired inflation models. In the latter case, fundamental superstrings produced in the very early universe may have stretched to macroscopic scales, in which case they are known as cosmic superstrings. If observed, these objects provide a unique window into the early universe and possibly string theory. Recent progress in CMB polarization and gravitational wave detection highlights how some of these scenarios could be constrained by high-resolution data. However, they also show that the current bottleneck is the lack of accurate high-resolution simulations of defect networks that can be used as templates for robust statistical analysis, implying that none of the current constraints is reliable. This will be an even bigger problem for next-generation facilities such as the SKAO and LISA. Moreover, most numerical simulations so far have been performed for the simplest Abelian-Higgs (or Nambu-Goto) model, while realistic cosmic strings will have non-trivial internal structure, including charges and currents. The scientific goal of the thesis is to fill this gap, continuing the deployment of a new generation of high-scalability defect evolution codes that will match the sensitivity of ongoing and forthcoming observational searches, and using them to develop and calibrate suitable analytic models. It will use both CAUP computational resources (including a GPU donated by NVIDIA) and world-leading HPC facilites accessed through PRACE/EuroHPC. The student should have an interest and relevant previous experience in computational physics, data analysis and visualisation. Experience of parallel and/or GPU programming would also be highly beneficial. The student will join a recently approved Paris-Porto-Cambridge collaboration grant.

Atomic inputs for probing the r-process in kilonovae

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1718 - Jorge Sampaio

Co-Supervisor: 1955 - Gabriel Martínez Pinedo

Co-Supervisor: 1946 - José Marques

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Física

Typology: Mixed

Abroad-Institution: GSI Helmholtzzentrum für Schwerionenforschung

In this proposal we intend to make a relevant contribution to the questions "Where are the heaviest elements in nature produced? And can we identify an astrophysical signature of their production?" We know that light elements like hydrogen and helium are produced at the beginning of the universe, about a few minutes after the Big-Bang, and that heavier elements up to iron are produced in nuclear fusion cycles inside stars. The mechanisms of production of elements heavier than iron have also been developed for many decades. Half of the nuclei heavier than Iron can be produced in stars from the asymptotic giant branch (AGB stars) through a neutron-capture process called s-process. The "s" comes from the slow capture rate of neutrons from seed nuclei, relative to the competing reaction of β-decay. The other half, including Thorium and Uranium, cannot be produced through this process Therefore, a more extreme process is required in which the rate of neutron capture is higher than the timescale of beta-decay. This process is called rapid neutron capture (or simply r-process). However, for such a process to occur, the environment must be extremely neutron rich. For that reason, core-collapse supernovae explosions were suggested as the main site for the production of r-process elements. Yet, despite many years of research into this scenario, models and observations have failed to show clear evidence that the r-process happens in core-collapse supernovae. On the other hand, the observation of a kilonova electromagnetic transient associated with the gravitational wave signal GW170817 provided the first direct indication that r-process elements are produced in neutron-star mergers [1]. Additional events are expected to be detected in the following years, representing a complete change of paradigm in r-process research, as for the first time we will be confronted with direct observational data. To fully exploit such opportunity, it is fundamental to combine an improved description of nuclear and atomic parameters with sophisticated astrophysical simulations to provide accurate prediction of r-process nucleosynthesis yields and their electromagnetic signals to be confronted with observational data. Tables of atomic parameters (level energies, excitation/ionization cross-sections and oscillator strengths between individual levels) needed to calculate stellar opacities have large gaps, or do not exist at all, for most elements relevant for the r-process. The student will systematically calculate these atomic parameters for the different ionization stages relevant at the density and temperature range found in the ejecta expansion in a kilonova. For this she/he will use the FAC and MCDFGME codes that represent today the state of the art in atomic structure calculations. The results will serve as input for modeling the luminosity curves of kilonovas beyond the local thermal equilibrium (LTE) approximation. The PhD. research activities will be developed at LIP (Laboratório de Instrumentação e Física Experimental de Partículas), Lisbon, Portugal and at GSI (Helmholtz Centre for Heavy Ion Research), Darmstadt, Germany. The student should be available to spend a period of about two years at the GSI to apply the obtained data to the simulation of luminosity curves for different kilonova formation and evolution scenarios. [1] Kasen D. et al, Origin of the heavy elements in binary neutron-star mergers from a gravitational-wave event, Nature 551:80 (2017) https://doi.org/10.1038/nature24453

Search for New Phenomena in the Top quark sector using Anomaly Detection in the ATLAS/LHC Experiment

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1717 - Rute Pedro

Co-Supervisor: 26 - Nuno Castro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program: MAP-Fis

Typology: National

The Standard Model (SM) of Particle Physics is notably descriptive and predicted new particles well in advance, from which the Higgs boson discovered at CERN's Large Hadron Collider (LHC) is a remarkable case. However, there is paramount evidence of the need for beyond-Standard Model (BSM) physics, namely to provide dark matter candidates, explain the matter/dark-matter asymmetry, address the hierarchy problem and others. The LHC has a rich program on searches for New Physics (NP) but clues from new particles or interactions have not yet arisen. Events with top-quarks may directly disclose new particles from SM extensions that mix with the top quark sector, either decaying into top-quarks or produced in association with it. Specific searches are performed, for instance, in events with a boosted top-quark and missing transverse energy, in the fully hadronic topology, to probe the single production of vector-like top-quarks or dark matter signatures at the LHC. However, these searches are guided by these specific NP signals and need a complementary strategy, independent of such assumptions. This proposal is to use anomaly detection (AD) techniques, such as (variational-) auto-encoders and Deep SVDD, to search for events that are unlikely to be compatible with the SM, ensuring that if new physics is present in LHC data, it will not be missed by a priori hypothesis. Events consisting of a boosted hadronic top-quark decay and missing transverse energy collected by the ATLAS/LHC experiment will be analysed. The Deep Learning model will learn SM physics from simulated data and then look for anomalous non-SM-like events in the real collision data. The impact of sources of theoretical and experimental uncertainties on the AD performance will be assessed and benchmark NP signals will be used as tests throughout the AD development. The project will be integrated into the ATLAS Portuguese group, and collaboration with several international groups is foreseen. Synergies with the LIP Competence Centre for Simulation and Big Data and with the LIP Phenomenology group will be explored, namely to investigate approaches for experimental result interpretability and recasting into theory exclusion limits.

Finite Temperature Quark-Gluon Vertex and its Phenomenological Implications

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 301 - Orlando Oliveira

Co-Supervisor: 462 - Paulo Silva

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program: Física

Typology: National

The quark-gluon vertex being a complex function it is a fundamental correlation function of Quantum Chromodynamics that is at the heart of all Particle Physics phenomenology. At zero temperature, it is characterised by twelve form factors that explain the formation of hadrons, including confinement and chiral symmetry breaking mechanisms, and the dynamical properties of hadrons that are measured experimentally and summarised in hadronic form factors, gpd, tmd, etc. At finite the temperature the number of factor factors that are required to describe the vertex is much larger. This project aims to study, from first principles using lattice QCD simulations, how this fundamental QCD vertex evolves with temperature by computing its form factors above and below the deconfinement temperature. Implications of the temperature dependence of the vertex phenomenology will also be explored. The quark and gluon propagators will also be investigated as a function of the temperature, playing particular attention to chiral symmetry breaking/restoration by looking simultaneously to the running quark mass and the masses of scalar and pseudo-scalar mesons. Hopefully, this will help the ongoing ultra-relativistic heavy-ion collision program at LHC and at RHIC and our understanding of the dynamics of the quark-gluon plasma.

Beyond the physics we know – searching for new resonances in ATLAS with Higgs and vector bosons

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 484 - Ricardo Gonçalo

Co-Supervisor: 1786 - Inês Ochoa

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: Doutoramento em Física / PhD in Physics

Typology: Mixed

Abroad-Institution: CERN

Despite its success in precisely describing particle interaction, the Standard Model of Particle Physics (SM) does not address many open questions about our Universe. Recent and future runs of the LHC of high-energy proton-proton collisions provide unique probes into the energy scales where answers may lie. A common prediction of SM extensions is the existence of new heavy particles, such as additional Higgs bosons, or W’ and Z’ bosons, which may couple preferentially to other bosons and have suppressed fermion couplings. This possibility motivates a dedicated search in the vector boson fusion production channel, for new particles that decay into W, Z and Higgs bosons. The student will develop a novel data analysis that will be uniquely sensitive to this final state signature.This search will complement the current results from the ATLAS collaboration that target new resonance searches via quark or gluon couplings. They will explore the LHC dataset at the high energy frontier and scrutinize a new corner of phase-space where new physics may be hiding. The PhD research work will be pursued in the international environment of the ATLAS collaboration, and part of it will take place at CERN. The student will be involved in the operation of the ATLAS experiment during data taking, profiting from the dataset to be collected in the 3rd experimental run of the LHC, from 2022 to 2024.

The partonic structure of hadrons

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1843 - Gernot Eichmann

Co-Supervisor: 1962 - Alfred Stadler

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

Almost all mass of visible matter rests in atomic nuclei and therefore in nucleons, which are complicated bound states of “partons”, namely quarks and gluons, the fundamental degrees of freedom in QCD. However, the structure of mesons and baryons is much more complicated than the naïve quark model suggests and their internal composition is still largely unknown territory. The distribution of quarks and gluons inside hadrons and nuclei, the decomposition of spin and orbital angular momentum, and the role of gluons in the dynamical generation of a hadron’s mass are all urgent questions that need to be answered. The experimental landscape in the forthcoming decades will be shaped by the COMPASS++/AMBER experiments at CERN and the Electron-Ion-Collider (EIC) at Brookhaven, which aim to map out the partonic structure of mesons, nucleons and nuclei and reveal the origin of the glue that binds their constituents. The central quantities of interest are parton correlation functions such as PDFs (Parton Distribution Functions), GPDs (Generalized Parton Distributions) and TMDs (Transverse Momentum Distributions), which encode the spatial and momentum distributions of partons and their spin and orbital angular momentum correlations inside hadrons. The goal of this project is to compute PDFs, GPDs and TMDs with nonperturbative continuum calculations by employing a new technique that has been recently established. This will deliver new insights on the internal structure of hadrons and provide much needed theory support for upcoming experiments at CERN and other facilities.

Reaching for PeVatrons with the future Southern Wide-field Gamma-ray Observatory

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 29 - Ruben Conceição

Co-Supervisor: 11 - Mário Pimenta

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Ph.D in Physics at IST (Doutoramento em Física no IST)

Typology: National

The observation of the high-energy gamma-rays provides a unique window to explore the extreme energy universe and fundamental phenomena related to it. The observation of these rare phenomena implies the construction of huge compact experiments and large areas, placed at altitudes of around 5000 meters above sea level. These experiments should be able to fight the enormous hadronic background to observe the gamma-rays. The recent observation by LHAASO of astrophysical gamma-rays with energies above PeV puts pressure to build a huge observatory with an area of at least 1 km^2 able to survey the galaxy in search of the origin of these fascinating messengers from the cosmos - the Southern Wide-field Gamma-ray Observatory (SWGO).

Di-Higgs production and the electroweak vacuum at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 484 - Ricardo Gonçalo

Co-Supervisor: 140 - Filipe Veloso

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: Doutoramento em Física / PhD in Physics

Typology: National

Since its discovery, the Higgs boson became a prime tool to search for physics beyond the Standard Model (SM). At the current level of precision, the Higgs boson is compatible with SM expectations. A number of open questions indicate the existence of new physics that could be unveiled as we explore the LHC data. A wealth of experimental results from the ATLAS and CMS experiments, probe the region around the minimum of the Higgs potential, or vacuum. But the shape of this potential is not constrained experimentally. This shape is intimately connected to the breaking of the electroweak gauge symmetry, which resulted in the fundamental forces we experience today. To experimentally constrain this shape we must measure the Higgs boson self-coupling, which is accessible at the LHC through the simultaneous production of two Higgs bosons. The selected student will join the Portuguese ATLAS team, working in close collaboration with theorists and integrated into our international collaboration. He or she will be able to contribute to enhancing our current knowledge in this important area, which will become one of the most important measurements of LHC experiments. The student will also employ the latest theory developments and the most recent advances in reconstruction techniques: from boosted object identification to machine learning. The successful student will be able to participate in the operation of the ATLAS experiment during the LHC Run 3 to start in 2022, and travel to CERN will be required.

Dark matter impact on gravitational waves

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 220 - Rui Santos

Host Institution: CFTC - Centro de Física Teórica e Computacional

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: PhD in Physics at FCUL

Typology: National

The existence of dark matter (DM) seems to be well established by observations from different sources. However, its nature is still a complete mystery. Even if DM comes in the form of a particle its mass range is barely constrained, with values for a gauge field of the order 10-21 eV to the TeV range. As an example, the constituents of Proca stars have masses in the low range of the spectrum with the exact value depending on mass of the star. At the other end of the spectrum we have the so-called Weakly Interacting Massive Particle (WIMP) of the order of the electroweak scale. It is a simple exercise in quantum field theory to build a model that contains one or more dark matter candidates. This candidate is not constrained in its spin nor in its mass. There are many dark matter experiments of direct and indirect detection and dark matter is also searched for at the Large Hadron Collider. But different dark matter candidates can have a different impact in the observation of gravitational waves. This work is about the comparison of models with different dark mater candidates in their contribution to specific patterns in gravitational waves.

The early universe as a window to particle physics

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 220 - Rui Santos

Co-Supervisor: 1956 - Milada Margarete Mühlleitner

Host Institution: CFTC - Centro de Física Teórica e Computacional

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: PhD in Physics at FCUL

Typology: National

The Large Hadron Collider (LHC) will soon start its third run at a center-of-mass energy of about 14 TeV. A myriad of models has been proposed and searches at the LHC will try to cover as much parameter space of each model as possible. Many of these models also solve the most important outstanding issues of the Standard Model: provide a Dark Matter candidate and reproduce the correct matter anti-matter asymmetry in the universe. Hence, the complementarity with experiments from cosmology, astrophysics and astronomy can be used. The main focus of this work is to study phase transitions in the early universe together with gravitational wave experiments and the baryon number asymmetry as a guide to restrict the parameter space of models and thus find hints that can point us in the right direction both at the LHC and at future colliders.

Higgs and top quark associated production to probe beyond the Standard Model with the ATLAS experiment

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 484 - Ricardo Gonçalo

Co-Supervisor: 1720 - Yvonne Peters

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: Physics

Typology: Mixed

Abroad-Institution: University of Manchester

After an intense search, the associated production of the Higgs boson with a top quark pair was finally observed in 2018. This production channel provides the best way to directly measure the coupling between Higgs and top, the heaviest fundamental particles in the Standard Model (SM). But it also provides a way to look beyond the SM, in particular to search for signs of a non-standard Higgs boson, leading to CP-violation in the Higgs sector. Such a component is well justified in scenarios like the two-Higgs doublet model, and finding it would constitute a major discovery. In particular, it could lead to understanding why there is a huge asymmetry between matter and antimatter in the Universe. In this leading edge research, the selected student will analyze data collected by the ATLAS experiment during the LHC Run 3, to start in 2022. He or she will have the opportunity to participate in the operation of the experiment at CERN. The student will integrate the Portuguese ATLAS team and will use recent techniques developed in our group to enhance the experimental sensitivity of the analysis. Part of the programme will take place at the University of Manchester, where the student will spend part of the time of the PhD as foreseen in the grant. Besides the Manchester group, the student would work in a vibrant international team within the ATLAS collaboration.

New Physics and Vector Like Fermions

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 19 - Joaquim Silva-Marcos

Co-Supervisor: 150 - Gustavo Castelo Branco

Co-Supervisor: 23 - Francisco Botella

Host Institution: CFTP - Centro de Física Teórica de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: PhD Program in Physics Engineering (PDEFT)

Typology: Mixed

Abroad-Institution: Universitat de València - IFIC

From the student is expected that he/she writes a PhD Thesis in the Field of physics Beyond the Standard Model, in particular Vector-like Fermions (VLF), based on original work published in the best international journals in the field, with focus on the quality and impact. The student is also required to participate in excellent international Schools and establish international contacts during Work-visits at CERN and other excellent Institutions and present his/her work at these events. The initial focus of the thesis will be on the study of models with VLFs, but the student will also be exploring models with multiple Higgs and others. The topics to be covered are, amongst other, the development and use of (new) concrete tools to test physics beyond the SM and explore NP models which are consistent with the Electro Weak Precision Measurements (EWPM) of the current and of future data, coming from LHC or others. In particular, we shall focus on very sensitive CP violation measuring parameters such as epsilon-K, epsilon’/epsilon or others, which will then severely restrict all kinds of various models and their content. In addition in our analysis of models, we will use other powerful tools based on weak-basis invariants. The CKM unitarity problem, is also an important problem which we will be addressing in the context of Vector-like Quarks (VLQ). At present, one of the main issues at the LHC is the search for new heavy fermions, e.g. quarks with masses beyond the top quark, as is the case of a heavy-top and which occurs naturally in models with VLQs in the up sector, or in the case of the leptons, the search for heavy Majorana neutrinos. With this in mind, we will be studying predictions for processes, possibly, to be witnessed at the LHC, as e.g. the decays of heavy-top T -> d W+. Thus, a strong interaction with experimentalists at LIP/CERN will be required. From the student it is expected that he/she acquires a very broad and deep formation in the fields of work proposed here.

Measurement of top quark rare decay t->sW at ATLAS

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 140 - Filipe Veloso

Co-Supervisor: 484 - Ricardo Gonçalo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: PhD in Physics

Typology: National

The top quark is the heaviest elementary particle known, with a mass close to the electroweak symmetry breaking, and it can provide clues about the symmetry breaking and the Higgs mechanisms. It is thus an excellent object to test the Standard Model of Particle Physics (SM). There is an important effort to study the top quark properties, like its mass, production cross-sections, electric charge, spin, decay asymmetries, rare decays, etc... Deviations from SM predictions of the production and decay properties of the top quark provide model-independent tests for physics beyond the SM. According to the SM, the top quark decays nearly 100% of the time to a W boson and a b quark. The Cabbibo-Kobayashi-Maskawa (CKM) quark mixing matrix is related to the rates of the Flavour Changing Charged Current (FCCC) decay modes. Some of the elements, e.g. Vts, were not yet directly measured but are determined from the unitarity conditions of the matrix. A direct measurement of these elements put strict conditions on the assumptions behind the matrix properties, as the existence of only three families on the SM. This research program will be developed within the Portuguese ATLAS group. It aims to measure the decay rate of the top quark into a W boson plus a s-quark with LHC data collected by the ATLAS detector using computational tools such as machine learning techniques. This result will then be used to measure the amplitude of the CKM element Vts. In addition the student will participate in the maintenance and operation of the ATLAS detector, namely in the calibration of the TileCal hadronic calorimeter. Short periods at CERN may also be required in order to collaborate in working meetings and/or shifts.

Black-hole-induced vacuum transitions in Two Higgs Doublet Models

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 794 - Pedro Ferreira

Host Institution: CFTC - Centro de Física Teórica e Computacional

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Doutoramento em Física, Faculdade de Ciências, Universidade de Lisboa

Typology: National

Models with larger scalar content than the Standard Model - such as the Two Higgs Doublet Model (2HDM) - can have several minima, but only one of those minima can be the "real" one. Black holes can work as catalysts between different minima, with potentially disastrous consequences. The parameters of the model must therefore be such that this vacuum transition is avoided. The constraints that one can therefore impose on the 2HDM, or other models, will therefore increase its predictive power and impact its LHC phenomenology. Can such constraints be so strong as to predict the masses and other properties of scalar particles that have yet not been discovered?

Development of high-performance timing detectors for the CMS forward proton spectrometer

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 144 - Joao Varela

Co-Supervisor: 802 - Jonathan Hollar

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: Mixed

Abroad-Institution: CERN

One of the major challenges of operating such detectors at the HL-LHC is the "pileup", or additional collisions occurring in the same proton bunch crossing as the collision of interest. By precisely measuring their time-of-flight, forward protons produced in these collisions can be correctly associated to the correct collision vertex, enabling rare photon-photon interactions to be reconstructed even at the maximum pileup foreseen for the HL-LHC. In order to fully resolve all collisions with forward protons, timing precisions of ~20ps or less will be of paramount importance, and enhance the sensitivity to these processes. During Run 2 of the LHC, proton fast timing detectors were already operated as a proof of principle, achieving resolutions of ~100ps with high efficiency. While these detectors were very resistant to radiation, they were limited, particularly by the TDC and related electronics, to timing resolutions of ~30-40ps per plane. For the HL-LHC, new technologies will be required to cope with the pileup, radiation, and event rates, both in terms of sensors and readout electronics. This project will help to address that challenge by exploring the latest developments in timing detectors and electronics, with the smallest possible segmentation and under extreme radiation conditions.

Expecting the unexpected: going beyond the standard searches at colliders

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 26 - Nuno Castro

Co-Supervisor: 341 - Miguel Crispim Romão

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program: MAP-Fis

Typology: National

A cornerstone of the Standard Model (SM) of Particle Physics is the formulation of the electroweak interactions as arising from a spontaneously broken gauge symmetry. Experiments over the past four decades have confirmed this hypothesis with precision, most notably the LEP and SLC collider programs. The ATLAS and CMS collaborations reported in 2012 observations of a new particle produced at the CERN Large Hadron Collider (LHC) possessing properties so far consistent with those predicted for the SM Higgs boson. It should be noted, nonetheless, that the exact nature of the symmetry-breaking mechanism is not yet determined. Furthermore, regardless of the many experimental validations of the SM, it is known that it cannot be regarded as a final theory, given the many problems it fails to solve, namely the hierarchy problem, the lack of a dark matter candidate, matter-antimatter asymmetry, and others. Attempting to solve these problems, many beyond the SM theories were built. Vector-like quarks (VLQ) are featured in some of these models, as spin 1/2 fermions, color triplets with the same left and right quantum numbers, mixing with SM quarks. Both the ATLAS and CMS experiments have developed a comprehensive search program for vector-like quarks. Nonetheless, and despite a significant effort to present general results, most of these analysis made important assumptions on the production and decay modes of the vector-like quarks and thus missing possible alternative signatures, which can have strong phenomenological motivations. The current proposal foresees the development and implementation of a search for vector-like quarks which can be produced in pairs via a heavy gluon or decay into new scalars. Given the multitude of final states that vector-like quark production can have, the search strategy will rely on the use of deep learning. A complete experimental analysis, considering a detailed study of the modelling of backgrounds and sources of uncertainties will be developed. The phenomenological consequences of the experimental results will be also be studied, in close collaboration with the Phenomenology group at LIP. The current proposal will be integrated in the Portuguese ATLAS team and collaboration with several international groups is foreseen.

Biocosmology: evolving state space and simulating the Adjacent Possible 


Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1781 - Andrew Liddle

Co-Supervisor: 1854 - Marina Cortês

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astrophysics

Typology: National

We are founding a new scientific discipline that we call Biocosmology. In an ongoing collaboration with Stuart Kauffman (Seattle) and Lee Smolin (Perimeter Institute, Canada), we are proposing a new way of viewing physical laws, particularly emergent phenomena, that can permit incorporation of biological systems into cosmological models. It is the first bridge connecting cosmology and biology, scientific areas which were previously disconnected though lack of a common mathematical framework and tools. Biocosmology allows us to see life through the lens of black holes, dark energy, and dark matter. It is the first quantification, ever, of the value of our planet before the vastness of the cosmos. One of the main principles is to allow for the possible evolution of the physical state space of the Universe, as it and its contained biospheres develop. This PhD project has the goal of investigating the consequences of such evolution both from a mathematical point of view through simulations, and from a physical point of view by connecting to ideas of information and entropy, particularly in connection with cosmic horizons.

Origin of the arrow of time of the Universe

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1854 - Marina Cortês

Co-Supervisor: 1781 - Andrew Liddle

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astrophysics

Typology: National

Time always moves in the same direction, it always increases and never decreases: we always remember the past and never the future. This asymmetry of time is universal, from scales on Earth up to cosmological scales. We receive light that galaxies emitted long ago in the past and never receive light they emitted in the future. This time asymmetry is not reflected in the majority of physics laws which are time symmetric, they work in the same way if time is increasing or decreasing. In fundamental physics time is symmetric, and we attribute the cosmological arrow of time to very unusual initial conditions in the beginning of the universe. These conditions are so special that their probability is of order 1 in 10^90. Why the universe started in such an unlikely state is a question we have no answer for in cosmology. In this work we investigate whether the time asymmetry may already be present in the fundamental laws, which would avoid having to attribute it to very special initial conditions at the Big Bang. We construct models that simulate such a time asymmetry and the student will run simulations with these models from existing code. The code for the simulations is already in place, so the student can directly start working on it. The goal is to infer from the results of the simulations what are the properties of physics if its are fundamentally time asymmetric. This project is co-supervised by Prof. Andrew R. Liddle of I.A, and by Prof. Lee Smolin of the Perimeter Institute for Theoretical Physics in Canada.

Testing the Dark Matter WIMP paradigm to the limit

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 220 - Rui Santos

Co-Supervisor: 1956 - Milada Margarete Mühlleitner

Host Institution: CFTC - Centro de Física Teórica e Computacional

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: PhD in Physics at FCUL

Typology: Mixed

Abroad-Institution: Karlsruhe Institute of Technology - KIT

The search for Dark Matter (DM) is one of the main goals of present high energy physics and astrophysics experiments. A large number of direct and indirect detection experiments together with searches at the Large Hadron Collider (LHC) have so far provided only bounds on the DM mass and couplings. DM candidates, which may be bosons or fermions, arise in many extensions of the Standard Model (SM) in a wide mass range. The objective of this work is to test the Weakly Interacting Massive Particle (WIMP) paradigm to the limit - will future experiments finally gives us a WIMP, or will we have to find a new paradigm? A special emphasis will be put on the planned XENONnT, DARWIN and SWGO experiments together with the high luminosity stage of the LHC and future colliders. Higher order corrections can change the limits obtained from the experiments for DM masses and couplings within each model. Moreover, it is possible that corrections to similar processes can have a much higher impact in say indirect detection than in direct detection. Therefore, only corrections to all processes involving DM in the three possible probing modes: direct, indirect and collider, can give us a clear idea of their importance. An important part of the work is to understand how the searches for DM at the LHC change when higher order corrections are considered; is it just a matter of number of events or will the distributions change? We expect to answer the question if we are definitely entering a very light/very heavy era for DM or if the WIMP is just in a moribund condition.

Tau lepton studies at the CMS experiment and at the future Muon Collider

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 1708 - Pedro Ferreira da Silva

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

This work will extensively investigate the tau reconstruction by means of new ML methods in two different environments at the CMS experiment at the LHC and at the new proposed Muon Collider. In the first case, data will be used to characterize tau lepton reconstruction. In the second case and due to the presence of the beam-induced background, a study of the tracking detector is also foreseen in order to maximize the exploitation of the time information in the silicon detector. Several options are possible, either measuring the time of each hit or having a dedicated layer in a strategic configuration. The algorithms will be studied on simulation and compared to CMS data. Using the new developed algorithms, the dedicated Higgs physics process will be reconstructed at CMS improving the current performance. They will be used to reconstruct the Higgs processes at the Muon Collider at the center-of-mass (CoM) energy of 3 TeV where the results will be compared to the those of the linear collider (CLIC). A CoM energy of 10 TeV is completely new and it has never been studied, and a brand new algorithm may be needed. Also at this energy the precision on Higgs boson couplings to tau leptons will be determined.

Vector Boson Scattering processes at the Large Hadron Collider

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 144 - Joao Varela

Co-Supervisor: 1708 - Pedro Ferreira da Silva

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

The high-energy scattering of massive electroweak bosons, known as vector boson scattering (VBS), is a sensitive probe of new physics. VBS signatures will be thoroughly and systematically investigated with the large data samples available and those that will be collected in the near future at the LHC. Searches for deviations from Standard Model (SM) expectations in VBS will be performed with the goal of testing the Electroweak Symmetry Breaking (EWSB) mechanism. Current state-of-the-art tools and theory developments, together with the latest experimental results and the studies foreseen for the near future will be studied, implemented, and integrated in the research program. New data analysis strategies to understand the interplay between models and the effective field theory paradigm for interpreting experimental results will be developed with the goal of probing existing Beyond the SM (BSM) models.

Probing the Standard Model with Forward Proton Tagging at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 802 - Jonathan Hollar

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

Central exclusive production (CEP) in high-energy proton-proton collisions provides a unique method to access a variety of physics topics, such as new physics via anomalous production of W and Z boson pairs, high transverse momentum (pT) jet production, top quark pairs, and possibly the production of new resonances. These studies can be carried out in particularly clean experimental conditions thanks to the absence of proton remnants. CEP of an object X may occur in the process pp → p+X+p, where ”+” indicates the “rapidity gaps” adjacent to the state X. Rapidity gaps are regions without primary particle production. In CEP processes, the mass of the state X can be reconstructed from the fractional momentum losses ξ1 and ξ2 of the scattered protons. At the LHC, the mass reach of the system X, MX, is significantly larger than at previous colliders because of the larger collision energy. The scattered protons can be observed mainly thanks to their momentum loss, due to the horizontal deviation from the beam trajectory. For the first time, proton-proton collisions at the LHC provide the conditions to study particle production with masses at the electroweak scale through photon-photon fusion. At the LHC energies in Run2 and in Run3, values of MX above 300 GeV can be probed. CEP processes at these masses have small cross sections, typically of the order of a few fb, and thus can be studied in normal high-luminosity fills.

Machine Learning and Measurements of Higgs boson properties

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 329 - Pietro Vischia

Co-Supervisor: 144 - Joao Varela

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: Mixed

Abroad-Institution: CERN

The discovery of the Higgs boson in 2012 was a major step towards improving the understanding of the mechanism of electroweak symmetry breaking (EWSB). With the value of the mass of the H boson now experimentally measured, the structure of the Higgs scalar field potential and the intensity of the Higgs boson self-couplings are precisely predicted in the SM. There are, however, compelling reasons to believe the SM is not complete. In particular, the LIP/CMS group is engaged in the study of SM and BSM processes to fully exploit the opportunities of the unparalleled energy of the LHC collisions. While measured properties are so far consistent with the expectation from the SM predictions, measuring the Higgs boson self-couplings provides an independent test of the SM and allows a direct measurements of the scalar sector properties. The self-coupling of the Higgs boson can be extracted from the measurement of the Higgs boson pair production cross section. A large amount of data of approximately 150/fb have been collected in Run1+Run2 and are available to study this process. With the upcoming Run3, additional 300/fb of data may become available in the next few years and there will be excellent opportunities for major discoveries in this domain.

Top quark physics and search for physics beyond the Standard Model at the Large Hadron Collider

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 1708 - Pedro Ferreira da Silva

Co-Supervisor: 144 - Joao Varela

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

Top quarks are abundantly produced in pairs at a hadron collider, and they constitute the main background to searches for New Physics. In the framework of the Standard Model (SM), each top quark decays into a W and a b quark. A good understanding of the top quark events will allow a more sensitive reach into the realm of searches for Beyond SM (BSM) processes. Recent checks of lepton flavour universality violation sparked a renewed interest towards measurements involving tau leptons, owing to a potential disagreement with SM predictions. The work will focus on studying the properties of the top quark dilepton final state and measure the tau and heavy flavour contents of top quark events. Studies of final states, including 3rd generation leptons and quarks such as tau leptons and b-jets, produced in association with top quark pair events may provide first hints for New Physics processes and shed light on the anomalies of Lepton Flavor Universality measurements. An anomalous flavor production is directly “visible” in this study. Deviations from SM predictions will indicate evidence for New Physics.

Free hyperboloidal evolution in axisymmetry

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1847 - Alex Vano-Vinuales

Co-Supervisor: 1848 - Edgar Gasperin Garcia

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

Intimately related to other areas of astrophysics and cosmology is the recently born field of gravitational wave (GW) astronomy. Crucial in the analysis of GW data is the input from numerical simulations in the form of waveform templates, which in turn carry the information from the physics in the strong field regime described by General Relativity (GR) via numerical simulations, from which the wave signals are extracted. As detector sensitivity increases, it needs to be matched by an improvement in the accuracy of the templates. One very promising and elegant way to get rid of finite-radius-extraction error is to numerically evolve the physical system of interest (e.g. a black hole binary) on hyperboloidal slices: spacelike slices that reach future null infinity, which corresponds to the endpoints of future-directed null geodesics and where global quantities of spacetimes such as energy or radiation are unambiguously defined. Conformal compactification, based on an idea by Nobel-laureate Penrose [1], is a suitable approach to the hyperboloidal initial value problem, further developed by Friedrich [2]. Formal divergences in the equations make numerical implementations of this problem challenging, but previous successful implementations encourage us to follow this promising path. The aim of this project is to generalise the existing free-evolution hyperboloidal spherically symmetric code [3] to axisymmetry, and so i) get closer to a full 3D hyperboloidal infrastructure to simulate binary coalescences and extract GW signals, and ii) couple the axisymmetric Einstein equations to physical content, such as scalar fields, the Maxwell equations and the Yang-Mills fields, to study their phenomenology in a scenario more general than spherical symmetry, and among them consider specially the candidates to fundamental fields. Additionally, the code can also be adapted to describe an Anti-deSitter (AdS) spacetime, and used to study collapse in axisymmetry. [1] Asymptotic properties of fields and space-times, Roger Penrose, Phys. Rev. Lett., 10:66–68 (1963). [2] Conformal Einstein Evolution, Helmut Friedrich, Lect. Notes Phys. 604 (2002), https://doi.org/10.1007/3-540-45818-2_1 [3] Spherical symmetry as a test case for unconstrained hyperboloidal evolution, Alex Vano-Vinuales, Sascha Husa and David Hilditch, Class.Quant.Grav. 32 (2015) 17, 175010, 1412.3827 [gr-qc].

Analytic Methods for Astrophysical Defect Fingerprinting

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program: MAP-fis

Typology: National

Cosmic strings arise naturally in many proposed theories of new physics beyond the standard model unifying the electroweak and strong interactions, as well as in many superstring inspired inflation models. In the latter case, fundamental superstrings produced in the very early universe may have stretched to macroscopic scales, in which case they are known as cosmic superstrings. If observed, these objects thus provide a unique window into the early universe and possibly string theory. Recent progress in CMB and gravitational wave observations shows how some of these scenarios can in principle be constrained by high-resolution data, but also highlight several bottlenecks which make current constraints unreliable. To fully exploit the potential of ESA facilities such as the SKAO and LISA, one needs matching progress both in high-resolution HPC numerical simulations of defect networks and in the analytic modelling of key physical mechanisms underlying their evolution, especially additional degrees of freedom on the defect worldsheets. This thesis will address the latter, using a series of novel mathematical and statistical techniques, informed by the world’s most accurate defect simulations (being done by the supervisor’s team) to build upon the successes of the canonical VOS model of Martins & Shellard to develop a new generation of accurately calibrated analytic models for general defect evolution as well as for their astrophysical fingerprints, which is able to match the sensitivity of ongoing and future observational searches and yield reliable constraints. The student will be a member of an ongoing Paris-Porto-Cambridge exchange grant.

Analysis of asymptotically flat and asymptotically de-Sitter spacetimes with conformal methods

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1848 - Edgar Gasperin Garcia

Co-Supervisor: 1847 - Alex Vano-Vinuales

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: PhD Physics

Typology: National

The asymptotic properties of spacetimes play a central role in many physical aspects of General Relativity (GR), in particular for the concept of gravitational radiation. One of the crucial concepts introduced for the realisation of the latter, was the use of conformal compactifications introduced in General Relativity by Roger Penrose to describe in a geometric way the notion of infinity. Arguably, the formulation that takes Penrose’s idea of conformal compactification --in conjunction with the theory of partial differential equations and the initial value problem-- to its ultimate consequences are, the Conformal Einstein Field (CEFE) equations introduced by H. Friedrich in [1]. These equations have been used for analytical purposes such as establishing (semi)-global non-linear stability results de-Sitter and Minkowski spacetimes and some partial global non-linear stability results for black hole spacetimes such as Schwarzschild-de Sitter [2]. Although these equations have been available since 1980 the numerical exploration of spacetimes using the CEFEs is still in its infancy compared with other formulations since they have not been systematically exploited as other formulations of GR. One of the alternatives to the CEFEs to reach the conformal boundary is the use of hyperboloidal foliations and scri-fixing techniques and more standard formulations of the Einstein Field Equations such as the Generalised Harmonic Gauge (EFE-GHG). These have also give fruitful results in combination with the weak null condition ---see [6]--- which can be exploited for numerical implementations [7] and for mathematical analysis [8]. By construction, hyperboloidal foliations reach the null-infinity but stays away from the region close to spatial infinity. The CEFEs on the other hand have access to this region via the construction of the so-called cylinder at spatial infinity. The latter has applications in terms of the calculation of asymptotic charges [4]. These methods, hyperboloidal and conformal, being complementary and grating access to the different regions of spacetimes can be exploited for the analysis of global properties of spacetimes by means of mathematical and numerical methods or a combination of thereof. ***The supervisor is currently working at University of Burgundy but will be joining soon Instituto Superior Tecnico Universidade de Lisboa under an FCT researcher contract*** [1] Friedrich H., On the regular and the asymptotic characteristic initial value problem for Einstein’s vacuum field equations, Proc. Roy. Soc. Lond. A 375 (1981) 169. [2] https://arxiv.org/abs/1506.00030 [3] https://arxiv.org/abs/1407.3317 [4] https://arxiv.org/abs/1608.05716 [5] https://arxiv.org/abs/1704.05639 [6] https://arxiv.org/abs/1812.06550 [7] https://arxiv.org/abs/1909.11749 [8] https://arxiv.org/abs/2101.07068

Challenging Lambda with Euclid and beyond

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program: MAP-fis

Typology: National

The growing amount of observational evidence for the recent acceleration of the universe unambiguously demonstrates that canonical theories of cosmology and particle physics are incomplete (if not incorrect) and that new physics is out there, waiting to be discovered. The most fundamental task for the next generation of astrophysical facilities is therefore to search for, identify and ultimately characterise this new physics. The acceleration is seemingly due to a dark component whose low-redshift gravitational behaviour is very similar to that of a cosmological constant. However, currently available data provides very little information about the high-redshift behaviour of this dark sector or its interactions with the rest of the degrees of freedom in the model. It is becoming increasingly clear that tackling the dark energy enigma will entail significantly extending the redshift range where its behaviour can be accurately mapped. A new generation of ESA and ESO facilities, such as Euclid, the ELT, and the SKAO have dark energy characterization as a key science driver, and in addition to significantly increasing the range and sensitivity of current observational probes will allow for entirely new tests. The goal of this thesis will be to carry out a systematic exploration of the landscape of physically viable dark energy paradigms and provide optimal discriminating observational tests. The work will initially focus on Euclid (whose launch is fast approaching) and will gradually broaden to explore synergies and probe combination with the SKAO and ANDES. The work will be done in the framework of the Euclid TWG, and the student will be a member of Euclid.

Fundamental cosmology from precision spectroscopy: The ESPRESSO road to ANDES

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program: MAP-fis

Typology: National

The observational evidence for the acceleration of the universe shows that canonical theories of gravitation, cosmology and particle physics are incomplete. The LambdaCDM model is a simple convenient approximation to a more fundamental theory, whose details or underlying principles are still unknown. Astrophysical facilities must search for, identify and characterise this new physics. My thesis will address this challenge, and specifically two questions: 1) Are the laws of physics universal? 2) What makes the universe accelerate? This relies on state-of-the-art high-resolution spectroscopy data from the ESPRESSO Guaranteed Time Observations, leading to the most accurate and precise such astrophysical tests, directly testing the Einstein Equivalence Principle and constraining dynamical dark energy. In parallel, I will participate in Phases B and C of construction of the ANDES spectrograph, specifically by optimizing its cosmology and fundamental physics science cases, including the exciting prospect of the detection of the Sandage test signal.

Unified equation of state consistent with astrophysical, gravitational, high- and low- energy nuclear physics data and its applications.

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 17 - Ilidio Lopes

Co-Supervisor: 2038 - Oleksii Ivanytskyi

Co-Supervisor: 1474 - Violetta Sagun

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Universidade de Coimbra

PhD Program: Physics

Typology: Mixed

Abroad-Institution: Institute for Theoretical Physics, University of Wroclaw

The compact astrophysical objects, i.e. neutron stars (NSs), hybrid (HSs) and quark stars (QSs), are the densest physical objects accessible by direct observations. Moreover, the physical processes inside objects like HSs and QSs, for which is expected that matter goes through a phase transition from nuclear matter to a quark-gluon plasma, are equally poorly understood. This limitation comes from the fact that QCD and its lattice formulation have very limited applicability at large baryonic densities which cannot allow for obtaining a reliable EoS. By imposing multimessenger constraints from GW physics and astrophysics, e.g. LIGO/Virgo/KAGRA Collaboration, NICER, SKA, etc, detection of QS or HS can become another scientific breakthrough and prove the existence of quark matter. The PhD project is focused on modeling the properties of HSs and probing the properties of phase transitions and the EoS of strongly interacting matter at high densities.

Jetography in Heavy Ion Collisions

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 30 - Liliana Apolinário

Co-Supervisor: 172 - Nestor Armesto

Co-Supervisor: 107 - José Guilherme Milhano

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Particle and Nuclear Physics

Typology: Mixed

Abroad-Institution: Universidade De Santiago de Compostela

Heavy-ion colliders provide ideal laboratories to explore Quantum Chromodynamics in extreme conditions, particularly the Quark-Gluon Plasma, a rapidly expanding, nearly perfect liquid that filled the early Universe. Due to its unique properties, it is the main object of study at ultra-relativistic heavy-ion colliders such as RHIC (BNL) and LHC (CERN). Jets – collimated sprays of hadrons with a common partonic origin – are produced concurrently with the collision. These objects traverse the extended medium, experiencing QGP-induced interactions (quenching), observed as modifications to jets’ initial energy and substructure. Spanning a wide range of scales, jets provide insight into QGP expansion. This proposal aims to study QGP evolution using jets, by extending current theoretical approaches to expanding media and constructing jet substructure observables sensitive to its time structure. This will provide constraints on existing hydrodynamical models and increased experimental control of heavy-ion data, essential steps towards a tomographic analysis of the medium.

Probing the nature of the neutrino with large scale dark matter detectors

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 464 - Alexandre Lindote

Co-Supervisor: 617 - Claudio Frederico Pascoal da Silva

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: Physics

Typology: National

Neutrinoless double-beta decay (0νββ) is one of the most important topics in modern particle physics, offering a unique opportunity to discover physics beyond the Standard Model. In a neutrinoless double-beta decay, a nucleus with mass number A and charge Z undergoes the decay (A, Z) → (A, Z+2) + 2e− but no neutrinos are emitted. This is not allowed in the Standard Model of particle physics as it violates the conservation of the lepton number, hinting that leptons play a part in the observed Universe matter/antimatter asymmetry. It would also probe the Majorana nature of neutrinos, i.e. if neutrinos are their own antiparticles, and would provide information about the neutrino mass hierarchy and effective mass. As such the observation of this process would be a breakthrough in modern physics. Xe-136, which comprises 9% of natural xenon, is one of the few isotopes that are expected to undergo this decay. This makes xenon detectors designed towards the search for dark matter particles extremely competitive in the search for this process, given their large masses and extremely low backgrounds, reaching sensitivities similar to dedicated experiments. LUX-ZEPLIN (LZ), which started operating in late 2021, is one of such detectors. Employing ten tonnes of liquid xenon, it contains a total of 630 kg of Xe-136 in its sensitive region. A preliminary study using simulated data showed that it could reach a half-life sensitivity of 1.06×10^26 years after 1000 days of operation, similar to the current best results. This study used conservative assumptions on the background assessment, energy resolution and background discrimination that can be significantly improved with real data. A next generation (G3) detector is already being planned, with a total mass up to 10x larger, which can lead to a sensitivity 100x higher than LZ, leading to the confirmation (in case of an observation) or exclusion of the inverted hierarchy for the neutrino masses.

Heavy baryon excitations with functional calculations: Confirming CERN discoveries and predicting new states

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1843 - Gernot Eichmann

Co-Supervisor: 302 - Teresa Pena

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

Our understanding of heavy baryons has expanded considerably in recent years with the discovery of many new states including charm and bottom quarks at the LHC. Heavy-baryon spectroscopy is now a cutting-edge area of research, and it is crucial to develop a theoretical understanding of such states from first principles in Quantum Chromodynamics (QCD). The goal of this project is to compute the spectrum of heavy baryons using functional methods in QCD, in particular the combination of Dyson-Schwinger equations and the three-body Faddeev equation which governs the behavior of baryons made of three valence quarks. These methods have been successfully employed in the light-baryon sector, and our aim is to extend them to charm and bottom baryons as well as for computations of their excitations and electromagnetic form factors. An important open question concerns relativistic effects which are crucial for light baryons, but recent studies suggest that relativity could also play in important role for charmed and even bottom baryons. As a key improvement, we will implement current progress in the calculation of QCD’s n-point correlation functions towards ab-initio calculations of heavy baryon spectroscopy and structure.

IDENTIFYING SIGNATURES OF HYBRID STARS

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 174 - Constança Providência

Co-Supervisor: 2033 - TUHIN MALIK

Co-Supervisor: 230 - Márcio Ferreira

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program: Doutoramento em Física

Typology: National

In recent years, observational capacities have increased enormously. Strong constraints were set on the equation of state (EOS) of dense matter combining the discovery of massive neutron stars (NS) with the results obtained by the LIGO-Virgo gravitational wave (GW) observations of NS mergers and from X-ray observations of pulsars, with the NICER mission. NSs are one of the most interesting laboratories of the Universe, allowing us to study aspects of fundamental physics unreachable otherwise. NS observations will allow us to determine the stellar matter EOS. A second problem is the determination of its constitution since similar EOS may describe different scenarios. The project will answer the question “is deconfined quark matter present in the NS core?”, by studying possible signatures of quark matter. Rotating and non-rotation hybrid star properties will be calculated from hybrid star EOS based on microscopic models. Statistical methods will be applied to distinguish different scenarios.

Neutrino phenomenology: a window to physics beyond the Standard Model

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 147 - Filipe Joaquim

Co-Supervisor: 2028 - Mariam Tórtola

Host Institution: CFTP - Centro de Física Teórica de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Doutoramento em Física

Typology: National

Neutrinos are very elusive particles which opened the window for physics beyond the Standard Model (SM) of electroweak interactions with the discovery of neutrino oscillations. With the confirmation of neutrino masses, there has been intensive activity in investigating the phenomenological consequences which stem from extending the SM such that neutrinos are massive. In this thesis several aspects related to neutrino physics may be covered. A more specific plan is to be decided together with the selected candidate and according to their possible interest in any neutrino-related topic.

The proposed work plan aims at giving a contributPhysics Beyond the Standard Model (BSM) in the Higgs and Flavour sectors

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 150 - Gustavo Castelo Branco

Co-Supervisor: 121 - Margarida Nesbitt Rebelo

Host Institution: CFTP - Centro de Física Teórica de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

The proposed work plan aims at giving a contribution towards uncovering what is the Physics Beyond the Standard Model (BSM) in the Higgs and Flavour sector of Particle Physics. These two sectors are intimately related from the theoretical point of view. The connection is established directly at the Lagrangian level. In the state of the art it is explained, why physics BSM is required. Symmetries increase predictability and will play a fundamental role in this work. Muti-Higgs models as well models with an extended quark and leptonic sector will be considered. The work will focus on the origin of fermion masses and mixing, on analysing how to suppress dangerous flavour changing neutral currents and on the study of new sources of CP violation. In some extensions good dark matter candidates will arise. At all stages the most recent experimental results will play a fundamental role in guiding the theoretical research.

The Effects of dark matter on hybrid stars and their thermal evolution

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 17 - Ilidio Lopes

Co-Supervisor: 1474 - Violetta Sagun

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

Recent detections of binary neutron stars (NSs) mergers [1,2] opened a possibility to study their internal structure and equations of state (EoS) of matter at supranuclear densities [3] through the gravitational waves (GW) emitted during their coalescence. The finite size and internal structure of NSs alter a GW signal. Hence, GW models describing the binary neutron star coalescence incorporate the tidal deformations, which, once measured, allow us to constrain the internal composition of these objects. On the other hand, compact stars may accumulate a sizable amount of dark matter (DM) in their interior. In Ref. [4,5] asymmetric dark matter (ADM) captured by NSs was shown to be able to significantly impact stellar density profile and mass-radius relation. An accretion of massive DM particles can significantly reduce the maximum mass of the host NS, while light DM particles can create a very extended halo around the NS leading not to a decrease, but to an increase of its visible gravitational mass. This analysis was performed for neutron stars composed of pure hadronic matter. However, due to the findings of Ref. [3] this seems to be an oversimplifying assumption. It is believed that in the core of compact stars matter could go through a phase transition from nuclear matter to a plasma of strongly interacting quarks. This type of star is called hybrid star. Depending on the properties of hadronic and quark matter EoSs the deconfinement phase transition may produce a visible feature in the GW signal and compact star properties. Thus, in Ref. [3] it was demonstrated that the tidal deformabilities and the I-Love-Q relation obtained for the GW170817 event support a strong phase transition to quark matter in the stellar interiors. Therefore, the study of DM admixed hybrid stars and their evolution with a further comparison with observational data will allow us to constrain the DM properties inside the compact stars and to place a limit on the DM sector of the Universe. The PhD project is focused on a study of the impact of DM on the properties of hybrid stars, their evolution, and stability against radial and non-radial oscillations. The main emphasis will be given to searches for the signatures of the presence of quark-gluon plasma in a core of compact stars and the effect of DM on it. The selected candidate will establish a bridge between astrophysics, nuclear physics and quantum chromodynamics. The thesis will be supervised by Prof. Ilídio Lopes, astrophysicist, from the CENTRA, Instituto Superior Técnico (Lisbon) and Dr. Violetta Sagun, theoretical physicist, from the University of Coimbra (Coimbra). References: [1] Abbott, B. P. et al. (LIGO/Virgo Collaborations), Phys. Rev. Lett. 119, 161101 (2017). [2] Abbott, B. P. et al. (LIGO/Virgo Collaborations), Astrophys. J. Lett. 892, L3 (2020). [3] Paschalidis, V. et al., Phys. Rev. D 97, 084038 (2018). [4] Ivanytskyi, O. et al., Phys. Rev. D 102, 063028 (2020). [5] Karkevandi, D. R. et al., Phys. Rev. D 105, 023001 (2022).

Applications of modified gravity in high energy astroparticle physics and cosmology

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 466 - Francisco Lobo

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astronomy and Astrophysics

Typology: National

From the experimental side, General Relativity (GR) has been successfully tested directly in the Solar System in its weak-field, slow motion regime. Binary pulsars, most notably the Hulse-Taylor system PSR 1913 C 16, allow for indirect tests beyond the Solar System. However, strong gravity tests are still scarse and gravity is tested poorly at the scale of galaxies and clusters, where Newtonian gravity breaks . This has led to the development of several modified theories of gravity to replace galactic dark matter. In fact, the discovery that the present expansion of the universe appears to be accelerated indicates that gravity may not be described by GR at large scales. To explain the cosmic acceleration, one needs to introduce an exotic negative pressure fluid, denoted dark energy, which constitutes approximately 70% of the energy content of the universe. Dark energy is thus an ad hoc solution to the problem of the present acceleration of the universe, and alternatives such as modified gravity have been explored. In fact, a plethora of modifications of gravity have been proposed as reliable alternatives to dark matter and dark energy. In the high-energy astroparticle physics regime, modified gravity could shed light on several outstanding problems in particle physics, such as the nature of dark matter, since its thermal production in the early universe may give rise to a relic density of the same order of magnitude of the present dark matter density. Particularly relevant in these scenarios could be the role played by modified gravity, as these theories predict a thermal evolution of the universe different with respect to one based on GR. More precisely, modified gravity predicts a modification/amplification of the expansion rate of the universe with respect to standard cosmology so that the thermal relics decouple with larger relic abundances. Consequently, the correct value of the relic abundance comes out from larger annihilation cross-sections. Other fundamental issues in the framework of modified gravity are related to the origin of the matter-antimatter asymmetry in the universe and Leptogenesis, as the matter-antimatter asymmetry is still an open problem of the particle physics and cosmology. Furthermore, mixing fields, vacuum fluctuations, neutrino oscillations, WIMPS, gravitational waves and the absolute value of the neutrino mass could be important tools to probe modified gravity. These issues will be explored in this project. The ultimate goal of the proposed research program is to devise viable modified gravity models that pass local tests, explain the dynamics of the Universe and are consistent with constraints from high-energy astroparticle physics, and thus offer a window into understanding the perplexing nature of the dynamics of the Universe and of gravity itself.

Modified Gravity in Cosmology and High-Energy Astroparticle Physics

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 466 - Francisco Lobo

Co-Supervisor: 167 - Pedro Avelino

Co-Supervisor: 1500 - Noemi Frusciante

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astronomy and Astrophysics

Typology: National

The fact that General Relativity (GR) is facing so many theoretical and experimental challenges, namely, the difficulty in explaining particular observations, the incompatibility with other well-established theories and the lack of uniqueness might be indicative of a need for new gravitational physics. Indeed, renormalization approaches to GR in the 1960s and 1970s clearly showed that counterterms must be introduced. These terms alter the theory significantly and transform the general relativistic second order field equations to fourth or higher order. This implies that extra degrees of freedom, in addition to the general relativistic spin-two massless graviton, need to be introduced. The corrections implemented by renormalization are at least quadratic in the curvature scalar invariant and were employed in inflationary models for the early universe. Considering a more general approach, when one tries to explore gravity from the high-energy regime and obtain low-energy physics, one does not recover GR. For example, adopting string theory as a full theory of quantum gravity, one gets a low energy limit that does not reproduce GR but instead provides a scalar-tensor theory of gravity. These latter theories were developed following initial suggestions by Dirac, Jordan, Fierz, and Thiery, culminating in the Brans-Dicke theory, which is the prototype of scalar-tensor theories of gravity. The original motivations for Brans-Dicke theory were rooted in the need to implement Mach’s principle, which is not fully incorporated in GR, in a relativistic theory of gravity. Indeed, dilaton fields and their nonminimal couplings to the spacetime curvature are unavoidable features of string theories, and are shared with scalar-tensor gravity. It seems, therefore, that first loop corrections or attempts to fully quantize gravity necessarily introduce significant deviations from GR and extra degrees of freedom. Thus, this motivates going beyond GR, from the high-energy theoretical point of view. In the high-energy astroparticle physics regime, modified gravity could shed light on several outstanding problems in particle physics, such as the nature of dark matter since its thermal production in the early universe may give rise to a relic density of the same order of magnitude of the present dark matter density. Particularly relevant in these scenarios could be the role played by modified gravity, as these theories predict a thermal evolution of the universe different with respect to one based on GR. More precisely, modified gravity predicts a modification/amplification of the expansion rate of the universe with respect to standard cosmology so that the thermal relics decouple with larger relic abundances. As a consequence, the correct value of the relic abundance comes out from larger annihilation cross-sections. Other fundamental issues in the framework of modified gravity are related to the origin of the matter-antimatter asymmetry in the universe and Leptogenesis, as the matter-antimatter asymmetry in the Universe is still an open problem of the particle physics and cosmology. Furthermore, mixing fields, vacuum fluctuations, neutrino oscillations, WIMPS, gravitational waves and the absolute value of the neutrino mass could be important tools to probe modified gravity. These issues will be explored in this project. The ultimate goal of the proposed research program is to devise viable modified gravity models that pass local tests, explain the dynamics of the Universe and be consistent with constraints from high-energy astroparticle physics, and thus offer a window into understanding the perplexing nature of the dynamics of the Universe and of gravity itself.

Enhancement of the measurement capabilities for the Pierre Auger Observatory

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 6 - Pedro Assis

Co-Supervisor: 29 - Ruben Conceição

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program: Eng. Física Tecnológica

Typology: National

LIP has been leading within the Pierre Auger Observatory, the development of a dedicated muon detector to develop the measurement capabilities of the Observatory, focusing mainly on the muonic component of Air Showers. Auger was built to give a significant contribution to the understanding of ultra-high energy cosmic rays (UHECR), their origin and nature, as well as to study particle interactions at such high energies. The data taken by Auger led to several breakthroughs in UHECR physics. A suppression of the CR flux above 5.5x10^19 eV is firmly established, and the fine structure of the spectrum starts to unveil. A dipolar asymmetry on the arrival directions has been observed, strongly supporting their extra-galactic origin. The CR composition at very high energies have been inferred from shower measurements, and its interpretation indicates an unexpected transition from proton to heavier elements above 3x10^18 eV. The collaboration has also a research program to estimate the hadronic interaction properties at the highest energies. One of the most intriguing results from this research area is the apparent muon deficit in predictions. Additionally, no hadronic interaction model can explain all the measured shower observables simultaneously. The obtained results present either an unexpected astrophysical panorama or even new physics at the highest energies. However, the above claim gets significantly undermined by the poor control over the shower description, i.e. over our understanding about hadronic interactions. This puts pressure on the study of the shower muonic component. Muons stem directly from the decay of charged mesons and can travel long distances being able to reach the ground. They are thus a direct link to the hadronic interaction activity within the shower. Auger has set up an upgrade program to increase the collected information for each shower. In this context, LIP is responsible for the installation of MARTA, a small array of RPCs under the WCD to perform a direct measure of the muons present at the stations. MARTA high-quality data will enable cross-calibration between different detectors and will be able to deliver physics muon measurements at E = 10^17 eV, which corresponds to the LHC centre-of-mass energy. Such measurements would allow univocal tests to the performance of high-energy hadronic interaction models. The work will be developed integrated into a multidisciplinary team which is responsible for the detector construction, commissioning, operation, data analysis, muon reconstruction and impact on the air shower physics. The candidate is expected to develop high-level analysis to tackle the so-called muon problem.

Lepton Flavour Universality

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Co-Supervisor: 1796 - Alessio Boletti

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Ph.D in Physics at IST (Doutoramento em Física no IST)

Typology: National

Lepton flavour universality (LFU) is deeply ingrained in the symmetry structure of the standard model (SM). Indeed, the SM gauge group SU(3)xSU(2)xU(1) is one and the same for all three generations of fermions. However, recent data provide strong evidence for departures from the LFU principle. Such departures are reported in b quark decays to charged leptons of different flavours (electron, muon, tau). The definite observation of LFU violation, in contrast to the SM expectation, would have far reaching implications. It requires the presence of new particles beyond the SM (BSM), such as new gauge bosons (Z') or leptoquarks (LQ). The thesis project explores LFU observables in the most sensitive b->sll quark transitions using CMS data. The thesis project has the potential to deliver the first observation of New Physics at the LHC.

Birds of a feather: seeking the earliest high-energy events in the Universe at the high- and low-energy ends of the spectrum

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 234 - José Afonso

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astronomy and Astrophysics

Typology: National

The existence of powerful Active Galactic Nuclei (AGN) has now been established well within the first Gyr of the Universe, through the observations of tens of optically or near-infrared selected Quasi Stellar Objects (QSOs) up to the currently highest redshift of z~8. Theoretical work has been developed showing how super-massive (M~10^9 M_sun) black holes can exist at such early epochs, depending on the unknown but necessarily quick assembly and growth from a suitable seed. To understand what are these supermassive black holes (SMBH) seeds, how they lead to early AGN activity and how relevant this is to the early galaxy and structure formation, it is fundamental to detect AGN activity at the highest redshifts, well within the Epoch of Reionisation. Surprisingly, the sensitivity already exists to find such sources at both extremes of the electromagnetic spectrum, X-rays and radio wavelengths, but all efforts to detect them have so far been unsuccessful. This is presumably due to their expected rareness, but certainly also due to the lack of understanding of the high-energy physical processes present in these youngest extreme sources in the Universe. While wide area surveys to be performed with future telescopes such as Athena (in the x-rays) and SKA (in the radio) will overcome the former limitation, the latter suggests correct identification of such ”rosetta stone” sources will remain challenging, as we are unable to optimise our observations and detection strategies to these sources. Taking advantage of the strong Portuguese participation in these two future international observatories, this PhD project will explore the synergies allowed by the combination of the unique capabilities of Athena and SKA for the exploitation of the earliest AGN activity. Following-up on our recent work (Amarantidis+2019), the student will explore state-of-the-art galaxy and SMBH formation and evolution models, analyse the physical processes they assume, and implement new recipes for X-ray and radio emission processes - taking into account the most recent advances in our understanding of black hole accretion physics. This will lead to improved methodologies for the selection of very high redshift AGN, which will be tested in current deep X-ray and radio surveys. Finally, such methodologies will be used to optimise Athena and SKA observing strategies for the detection of the earliest examples of AGN activity.

Studying the origin of the elements with radioactive ions at ISOLDE/CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 500 - Daniel Galaviz Redondo

Co-Supervisor: 2034 - Francisco Javier Ferrer Fernández

Co-Supervisor: 2036 - Ángel Miguel Sánchez Benítez

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Ph.D. in Physics (Nuclear and Particle Physics)

Typology: National

Nuclei are the DNA of the cosmos [Woo03]. The understanding of the most basic characteristics that govern the strong, weak and electromagnetic interactions at the nuclear scale is of crucial importance to explain how our universe was formed and how it is evolving, how stars are born and die, and ultimately, how life came to exist. Powered by the energy released in its hot core, stars produce the largest bulk of natural appearing nuclei directly via nuclear fusion reactions [B2FH]. Beyond the iron natural abundance peak, heavier elements are produced predominantly via neutron capture reactions in the framework of the r-process [Thi11] and the s-process [Bus99]. Only a small fraction of stable isotopes located at the proton-richer side of the valley of beta stability, the so-called p-nuclei, cannot be synthesized through the previously mentioned processes. In the stellar environment provided by core-collapse and thermonuclear supernovae, the astrophysical p-process is the most established scenario for the production of the p-nuclei, which are synthesized via different photodisintegration paths starting on heavier nuclei and predominantly involving unstable nuclei [Arn03,Pig16]. In the framework of the present project, the PhD candidate will execute the first experiment that will determine the shape of the alpha-nuclear potential of radioactive isotopes (108,110)Sn located on the p-process nucleosynthesis path via the measurement of the elastic scattering angular distribution of alpha particles in inverse kinematics. This experiment will be possible thanks to the high intensity post-accelerated radioactive Sn beams available at the HIE-ISOLDE facility at CERN, combined with the recently developed technology of nuclear target production with high concentrations of helium nuclei [God16]. The supervisors of the present PhD program have led the international collaboration that recently proposed the innovative approach to the INTC (ISOLDE and Neutron Time-of-Flight Experiments Committee). The evaluation of the proposal was very positive, the INTC experts highlighted its scientific interest and its technical feasibility, and the full requested beam time was approved. The scheduling of the beam time is expected from July 2022 onwards. The scientific motivation of the proposed experiment lies in the fact that the uncertainties in the knowledge of the alpha-nuclear potential in the heavy regions of the nuclide chart constitute the main source of uncertainty in the production of the heavy stable p-nuclei [Rap06, Rau06, Rau16,Sim17]. Despite the various experimental efforts done over the past decades to reduce these uncertainties of this fundamental nuclear quantity (elastic scattering [Moh97,Zso01,Orn15], capture reactions online [Sch20] or through activation techniques [Hal12,Kis11]), these studies have always been limited to stable isotopes. Network calculations had to rely on the extrapolation of the theoretical models towards unstable nuclei [Arn03,Rau16]. The PhD candidate will analyse the first data available in unstable isotopes, opening the door to the reduction of the uncertainties in the modelling of the astrophysical p-process.  The present PhD program will be supported by the approved research project CERN/FIS-PAR/0009/2021. References: [Arn03] M. Arnould and S. Goriely. Phys. Rep. 384, 1 (2003) [B2HF] M. Burbidge, et al. "Synthesis of the Elements in Stars", Rev. Mod. Phys. 29, 547 (1957) [Bus99] M. Busso, R. Gallino, and G. J. Wasserburg, Annual Review of Astronomy and Astrophysics 37, 239 (1999) [God16] V. Godinho, et al.. ACS Omega, 1, 1229 (2016) [Hal12] Z. Halász, et al., Phys. Rev. C 85, 025804 (2012) [Kis11] G. Kiss, et al., Phys. Lett. B 695, 419 (2011) [Moh97] P. Mohr, et al., Phys. Rev. C 55, 1523 (1997) [Orn15] A. Ornelas, G. G. Kiss, P. Mohr, et al., Nucl. Phys. A 940, 194 (2015) [Pig16] M. Pignatari et al. International Journal of Modern Physics E 25, 1630003 (2016) [Rap06] W. Rapp, et al., Astrophys. J. 653, 474 (2006) [Rau06] T. Rauscher, Phys. Rev. C 73, 015804 (2006) [Rau16] T. Rauscher, et al., Monthly Notices of the Royal Astronomical Society 463, 4153 (2016) [Sch20] P. Scholz, H. Wilsenach, H. W. Becker, Phys. Rev. C 102, 045811 (2020) [Sim17] A. Simon, et al., J. Phys. G: Nucl. Part. Phys. 44, 064006 (2017) [Thi11] F.-K.Thielemann, et. al. Progress in Particle and Nuclear Physics 66, 346 (2011) [Woo03] S. Woosley, et al., "Nuclear data needs for the study of nucleosynthesis in massive stars", Nucl. Phys. A 718, 3 (2003) [Zso01] Zs. Fülöp, Gy. Gyürky, Z. Máté, et al., Phys. Rev. C 64, 065805 (2001)

Novel fast timing high resolution detector concept with four-dimensional capability for neutron science

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 1712 - Luís Margato

Co-Supervisor: 1719 - Andrey Morozov

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: Doutoramento em Física

Typology: National

Integrated in sophisticated instruments at large scale facilities (LSF), such as ILL- Institut Laue-Langevin (FR), ISIS - Neutron and Muon Source (UK), FRM II - Research Neutron Source Heinz Maier-Leibnitz (DE) and the ESS - European Spallation Source (SE), the neutron detectors enable to determine the positions of hydrogen and deuterium atoms in crystal structure, needed to reveal structural and dynamic aspects of the matter using neutrons as a probe, such as, e.g., of biological systems, nearly invisible using X-ray methods. However, the present state-of-the-art detectors cannot fully satisfy the tight requirements of the next generation instruments planned for the ESS and future spallation sources as well as of the upgrade programs of the existing large-scale facilities (LSF). For example, new instruments for reflectometry, small-angle neutron scattering (SANS) and macromolecular crystallography require detectors capable to provide simultaneously high detection efficiency, low gamma sensitivity, time resolution down to 0.1 µs, sub-millimeter spatial resolution and counting rate up to MHz/cm2. Ultra-high spatial resolution (~0.2 mm) is especially important for investigation of the structure of protein crystals of sub-millimeter size by neutron macromolecular crystallography. The capability to characterize samples of such small size is required since the growth of larger size crystals of biological macromolecules is very challenging. The same detector should also provide TOF capability with sub-microsecond time resolution, required to conduct high-precision wavelength-resolved measurements at the spallation neutron sources. Another example where the current neutron detection technologies are not adequate is in MIEZE neutron spin-echo spectroscopy, which is a novel method with ultra-high energy resolution for studies of ferromagnets, superconducting vortex lattices, and magnetic skyrmion systems. MIEZE requires neutron detectors with response time below 1 µs, very well-defined detection planes and high spatial resolution. The thesis programme is focused on the development of a novel detector concept, nRPC-4D, which offers four-dimensional readout capability (XYZ and time) and is intended for time-of-flight (TOF) neutron diffraction/reflectometry and energy- and time-resolved neutron imaging. The nRPC-4D concept combines two technologies: t-RPC (timing resistive plate chamber) invented in LIP for high energy physics applications and, to give RPCs the capability to detect thermal neutrons, B4C neutron converters enriched in boron-10 isotope developed jointly by the University of Linkoping and ESS. One main goal is to develop a detector demonstrator which can offer high time and spatial resolutions, good detection efficiency, high counting rate and low sensitivity to gamma rays. This PhD programme provides a unique opportunity for the candidate to be fully embedded in a strong international collaboration with the detector groups from the world-leading neutron facilities in Europe (ISIS, ILL, FRMII and ESS), opening a path to the next stages of the scientific career. Experimental campaigns to test the detector prototypes at the large-scale neutron facilities are also foreseen during this PhD programme implementation.

Equation of state of hot non-homogeneous neutron star matter

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 174 - Constança Providência

Co-Supervisor: 1710 - Francesca Gulminelli

Co-Supervisor: 1709 - Helena Pais

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program: Doutoramento em Física

Typology: Mixed

Abroad-Institution: Laboratoire de Physique Corpusculaire de CAEN - University of Caen

Light nuclear clusters are expected to be ubiquitously present in astrophysical environments and play an important role in different astrophysical phenomena involving ultra-dense baryonic matter, but the estimation of their abundance demands to correctly estimate the in-medium modification of their binding energy. This can be achieved in a phenomenological way, if theoretical models are calibrated to experimental data from heavy-ion collisions in the Fermi energy regime, where these same clusters are produced in comparable density and temperature conditions. The present project aims at building a calibrated low density equation of state via a direct collaboration between theory and experiment . A Bayesian inference approach will be applied within a relativistic mean field formalism to build a set of equations constrained by observations and experiments for the whole range of densities of interest. A complete equation of state (EoS) appropriate to describe hot neutron stars will be built and made available.

Collapse or collide: improved analysis of black hole formation mechanisms

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1735 - Jorge Rocha

Co-Supervisor: 958 - David Hilditch

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Programa Doutoral em Física

Typology: National

For several decades black holes have played a central role in theoretical physics, and the last few years revealed they are more than constructs of human imagination: we can actually observe them. In the context of general relativity, we have a very good understanding of how black holes are formed under gravitational collapse. Furthermore, there is a clear picture about how black holes can result from high energy collisions. However, this knowledge is based on the assumption that gravity is described exactly by general relativity, even at scales where we would naturally expect quantum gravity to take over. In addition, so far all (semi-)analytic studies of black hole formation processes are unrealistic in the sense that they adopt, at best, perfect fluids to describe the matter involved. This project proposes to take studies of gravitational collapse and shock wave collisions to the next level. On the one hand, relativistic elastic bodies will be considered in gravitational collapse and the impact of the matter’s elasticity in critical collapse and high energy collisions will be assessed. On the other hand, we will also study the effect of higher curvature corrections to general relativity on critical collapse. Such modifications to gravity are expected to leave imprints on critical collapse, since this subject deals with the formation of black holes at arbitrarily small scales. Gravitational collapse in the near critical regime is particularly relevant to understand the distribution of primordial black holes and to investigate the production of very massive hypothetical particles as products of Hawking radiation. Thus, while the research program is tailored to improve our present knowledge concerning black hole formation, it has also important implications for beyond-standard model physics and cosmology.

Probing CP couplings in ttX production at the Run3 of the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1728 - Antonio Onofre

Co-Supervisor: 58 - Miguel Fiolhais

Co-Supervisor: 484 - Ricardo Gonçalo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: Doutoramento em Fisica

Typology: National

In this PhD thesis proposal, we explore CP discrimination, in the associated production of top-quark pairs with generic scalar/pseudo-scalar and vector/axial-vector boson mediators, at the LHC. In addition to the Higgs boson, that may reveal a non Standard Model (SM) CP nature of the couplings to heavy quarks, these searches are also looking for hints of Dark Matter (DM) candidates, in simplified models with spin-0 and spin-1 particles, that act as mediators. Events from the associated production (ttX, X=spin-0, spin-1) of top quarks are searched for, in proton-proton collisions, at the Run3. A dedicated analysis for top quark pair production decaying to leptonic events with final states with at least one charged lepton and at least two jets from the decays of top quarks, is expected to be developed. Full kinematic event reconstruction is performed using a specific fitter which will be able to reconstruct the four momenta of the undetected neutrino(s), originated in the top quark decays. Following kinematic reconstruction, a search for specific angular distributions that are sensitive not only to the absolute value of the mediator CP couplings, but also to the signal (+ or -), is expected to be performed with the aim of discriminating, as well, the dominant backgrounds at the LHC from the signals under study. The mass range covered by the searches, start at low masses (order GeV) and goes to the high mass region (order TeV), passing through the Standard Model Higgs boson mass, used as a benchmark for the CP observables performance, developed during the course of this thesis. The use of Machine Learning algorithms for event classification, in particular to discriminate signals from background events, is also expected to be performed as, in the context of high energy physics, the use of ANNs in Deep Learning algorithms for event classification, has started to show particular promise in ttX with a completely new coverage of the CP parameter space. The impact on the signal sensitivity is to be quantified, using ATLAS data collected at the Run3, either as cross section and angular distributions measurements, in case of discovery, or by setting limits at 95% Confidence Level (CL), in case no New Physics is found. Monte Carlo generators, including MadGraph5_aMC@NLO with specific UFO models, are expected to be used to generate the different signals, at the RUN3 of the LHC.

Machine Learning Methods to improve the Phase II ATLAS Trigger system

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 55 - Patricia Conde Muino

Co-Supervisor: 1786 - Inês Ochoa

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: PhD In Engineering Physics

Typology: National

Polarimetry with AMEGO Space Observatory

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 156 - Rui Curado da Silva

Co-Supervisor: 326 - Jorge Maia

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program: IDPASC

Typology: National

Polarized gamma-ray emissions over 1 MeV were never observed. The most energetic polarized emissions recorded were obtained by ESA INTEGRAL. By measuring the polarization angle and degree of linear polarization of the gamma-ray sources, it will be possible to obtain two additional observational parameters thereby allowing better discrimination between various models explaining the operation of emission sources. Polarimetric observations can provide important information about geometries, magnetic fields, composition and emission mechanisms in a wide variety of gamma-ray sources such as: pulsars, solar flares, active galactic nuclei, galactic black holes or gamma-ray bursts. AMEGO is a large satellite (1.2 tons payload) based on Si trackers, with a calorimeter composed by arrays of 3D CdZnTe (CZT) and of CsI scintillator detectors that will operate in the Compton (0.2 - 10 MeV) and pair conversion (10 MeV - 10 GeV) regimes. It should provide unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, AMEGO will open a new window on the non-thermal Universe. Our group will take part in the development of AMEGO scientific instruments by participating in the respective simulation and experimental testing. The AMEGO space mission should provide e+/e- pair production based polarimetry in the MeV and our group will be responsible for the polarimetric characterization of a small scale AMEGO prototype to be performed at the Duke University synchrotron accelerator and as well during a prototype for a balloon born experiment to be launched in Palestine, Texas.

Anomaly detection in the search for new physics with the ATLAS detector

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1786 - Inês Ochoa

Co-Supervisor: 55 - Patricia Conde Muino

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

The Standard Model of Particle Physics (SM) is a very successful and precise description of particle interactions, yet it leaves unexplained several observable phenomena, such as gravity or dark matter. To address the open questions in the field, various extensions of the SM have been proposed, which typically predict the existence of new heavy particles with masses in the TeV scale. A vast program of searches by the ATLAS and CMS experiments at the LHC has, however, placed very strong constraints on the landscape of possible models for new physics. As a consequence, anomaly detection methods have been gaining ground, as part of a strategy to ensure a thorough and model-agnostic approach to new physics searches, expanding their potential and sensitivity to unexpected new signals. In this project, the student will take part in the ATLAS Collaboration program for new physics searches and explore the ATLAS dataset at the high energy frontier, including the wealth of data that is expected from the Run 3 of the LHC.

Dark Matter Effective Field Theories in Stellar Astrophysics

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 17 - Ilidio Lopes

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

The study of the Dark Matter (DM) phenomenology inside stars has already proven to be an important alternative way to study DM models. Its premise relies on the fact that Dark Matter particles in the vicinity of a star can be gravitationally captured by its massive gravitational field. There, DM particles will seldom interact with baryonic nuclei, serving as additional energy injection and transport mechanisms, which in some cases can lead to important effects in the stellar structure, causing considerable departures from the standard picture of stellar evolution. Using Asteroseismology, the study of stellar oscillations, as a diagnostic, we can constrain Dark Matter models leading to observables in contradiction with experimental observations.

Unravelling Physical Equations from Particle Experiments and Surveys using Symbolic Machine Learning

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 226 - Antonio da Silva

Co-Supervisor: 1861 - Alberto Krone-Martins

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Physics - Astronomy FCUL

Typology: National

Particle Physics and Cosmology are presently based on the construction of physical theories that are compared against observations to constrain model parameters. Despite the success of this paradigm, there is growing evidence of parameter tensions arising from the combination of observable properties and an increasing number of high-quality datasets. These tensions can be interpreted as opportunity windows for new physics, but that does not necessarily imply a deeper understanding at the more fundamental level. An alternative approach that could avoid tensions by construction is to let datasets to reveal their preferred laws, and then proceed with an interpretation at a more fundamental level envisioning the construction of consistent physical theories, without a priori assumptions. The overall objective of this project is the development, implementation and deployment of novel algorithms based on symbolic regression and machine/deep learning innovations emerging in the literature to infer data-driven expressions and seek model-independent information directly from cosmological data (see e.g. arXiv:1905.11481). In this project we will also study the application of these methods to derive the underlying profiles of halos, voids and the universe’s mean background density, and to confront these with theoretical predictions that rely on untested model assumptions about Dark Matter, Dark Energy and the Cosmological Principle.

Fast Electronics for the High Granularity Timing Detector of the ATLAS Experiment

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 484 - Ricardo Gonçalo

Co-Supervisor: 6 - Pedro Assis

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: PhD in Physics Engineering at IST (Doutoramento em Engenharia Física Tecnológica no IST)

Typology: National

The High Granularity Timing Detector will be an essential piece of the upgraded ATLAS detector for the high luminosity LHC phase. It will allow to suppress the background due to proton collision pileup, and so allow to achieve the ATLAS physics goals. This new detector will require a timing resolution of around 30 ps per charged particle track, obtained with the recent Low-Gain Avalanche Detector technology. These highly granular detectors will be read out using a new ASIC (ALTIROC) which is under development. The successful candidate will be integrated into the international team contributing to the development of the ALTIROC chip, a state of the art readout ASIC that will be at the heart of a new detector for the ATLAS experiment at the LHC. ALTIROC will need a very good timing resolution, of the order of 50 ps, and high charge sensitivity of about 2 fC, making this ASIC a challenging but crucial component of the experiment.

LHC Anomalies and New Physics

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Co-Supervisor: 1796 - Alessio Boletti

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Ph.D in Physics Engineering at IST (Doutoramento em Engenharia Física Tecnológica no IST)

Typology: National

The LHC physics program so-far has been extremely successful. It has established the standard model (SM) of particle physics as a superb theory. The SM cannot however be the ultimate theory of Nature, and a major goal of the LHC for the coming years is to detect the new physics (NP) that lies beyond the SM. The most significant and exciting indications of such NP, in all of the current collider data, lie in what is referred to as the “flavour anomalies”. These have persistently emerged from the data of various experiments, with their significance enhanced considerably recently at the LHC. They are detected through measurements of b-quark decays involving leptons. Such processes are highly sensitive to the presence of NP particles. The most favoured theoretical NP candidates addressing the anomalies would be LeptoQuarks (LQ) and new Gauge bosons (Z'). Even if those NP particles happen to be very heavy (and can thus not be produced directly in the LHC collisions), they do contribute as intermediary states (thanks to Quantum Mechanics) and their presence becomes experimentally accessible in measurements of these highly sensitive physics processes.

Testing the nature of light and ultralight FIP dark matter with deep learning

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1693 - António Morais

Co-Supervisor: 1713 - Felipe Ferreira de Freitas

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program: MAP-Fis

Typology: National

This thesis proposes a synergy between the areas of strong gravity, cosmology and particle physics in order to explore the FIP dark-matter paradigm. The deep-learning techniques necessary for these studies will be based on evolutionary optimization algorithms and computer vision methods recently developed both in the context of particle and gravitational wave identification. Contrary to the typical approach taken by the strong gravity community, this thesis aims at the construction of concrete particle physics models where ultralight DM particles can emerge either as pseudo-goldstone bosons or as vector bosons such that they can reveal themselves in the form of stable halos around compact astrophysical objects. However, such halos are only viable when the Compton wavelength of the field approximately matches the gravitational scale of the compact object. For the known astrophysical objects, such as black holes, whose mass ranges from 1-10^10 solar masses, this means that such bosonic particles must have masses between 10^{-10}-10^{-20} eV. The presence of an ultralight bosonic sector implies further bosonic particles that are not necessarily ultralight, although can still be dark. Furthermore, for models featuring neutrino mass generation mechanisms, a sterile neutrino can also become fermionic DM candidate with masses in the keV-MeV range. In this thesis, a catalog of models that can consistently predict light and ultralight bosons as well as sterile neutrinos will be constructed. These are extraordinary candidates to offer multi-component DM candidates which will be studied and confronted with data both from the gravitational and direct detection channels.

Collider and Gravitational probes for New Physics in Multi-Higgs Models

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1693 - António Morais

Co-Supervisor: 1713 - Felipe Ferreira de Freitas

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program: MAP-Fis

Typology: National

With the recent observation of gravitational waves (GW) by the LIGO-VIRGO collaboration and the Large Hadron Collider (LHC) RUN-3 scheduled to start at the middle of 2021 with twice the nominal luminosity and a center of mass energy of 14 TeV, a great opportunity for New Physics searches following a multi-messenger philosophy has emerged. In particular, models with extended scalar sectors feature the possibility of first order phase transitions (PT) capable of generating a stochastic background of primordial GW which, if detected, can become a gravitational portal and a probe for Beyond the Standard Model (BSM) physics. The LISA mission will offer a range of frequencies well into the mHz region, relevant for the electroweak (EW) PT. The non-trivial structure of such extended scalar sectors allows for multi-step phase transitions and corresponding GW signatures. This information, in synergy with collider physics, can offer complementary information on the quest for hints of a more complete description of particles and interactions. In this thesis we will consider models with additional electroweak Higgs doublets and singlets, supplemented by additional flavour or gauge symmetries, whose breaking takes place not far from the EW scale. We will investigate which particular BSM signatures are expected at the LHC for different benchmark models and how can this information be complemented by the stochastic background of GW, with focus on the future LISA mission. We will also consider models where vector-like fermions, extended neutrino sectors as well as composite Higgs scenarios will be studied along the same research strategy. These studies involve the development of intelligent algorithms based on Evolutionary searches for Deep Learning and Model Agnostic Meta-Learning (MAML). Such techniques can be used as a “control” environment for Monte-Carlo event generator software tools, such as MadGraph, Pythia and CosmoTransitions. One consequence of using these techniques is the possibility to accelerate the task of simulating data points for a given specific model. Simulations provided by MadGraph, Pythia and CosmoTransitions are rather CPU intensive and demand a fair amount of time to provide a significant statistics. One possible way to speed up the computation is to use Deep learning techniques, such as MAML, in order to capture the underlying features inherent of a given BSM scenario while leveraging such features to sample points more efficiently.