Call

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 the 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.

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.

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.

Dark energy and neutrino masses

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 633 - Nelson Nunes

Co-Supervisor: 1497 - Tiago Barreiro

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

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astronomy and Astrophysics

Typology: National

The standard cosmological model with a cosmological constant and cold dark matter (LCDM), though very successful, has started to show some weaknesses, not only theoretical (the so-called fine tuning and coincidence problems) but also observational (different datasets seem to give different values for the current expansion rate of the Universe and different values for the amplitude of collapsed structures at a given scale). Among the list of possible alternatives, scalar field models of dark energy stand out for their simplicity and for being present in all particle physics models. Nonetheless, they must interact with other particles, giving rise to new forces between matter particles. These interactions are tightly constrained for baryons, from gravitational experiments on Earth and the solar system. However these forces are not so constrained for interactions involving neutrinos or dark matter where current bounds come from cosmological observations. In fact, recent literature puts forward a mechanism to alleviate the Hubble tension by means of a scalar field coupled to neutrinos. This project aims at testing these proposals via both theoretical and cosmological data analysis approaches.

Unravelling Physical Equations from Cosmological and High-Energy Physics Datasets 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: Programa doutoral em Física e Astrofísica

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 the present “Concordance” Cosmological Model, there is growing evidence of parameter tensions between Cosmological Probes, depending on the origin dataset. These tensions can be interpreted as opportunity windows for new physics, however, that does not necessarily imply a deeper understanding at the more fundamental level. Alternatively, tensions can be avoided, by construction, if we allow datasets themselves to reveal their preferred laws, without a priori assumptions. In this PhD project, we propose to extract some of these laws directly from data. We will develop, implement and deploy novel algorithms based on symbolic regression and machine/deep learning innovations emerging in the literature to infer data-driven equations and model-independent information directly from cosmological and High Energy Physics (EP) data. We will then apply these methods together with modern astronomical survey data from ESA Gaia and Euclid to derive the underlying profiles of halos, voids and the Universe’s mean background density. This analysis will enable us to confront theoretical predictions that rely on physical model assumptions, including from Particle Physics, about the nature of Dark Matter, Dark Energy and the Cosmological Principle, with the profiles derived from model-independent data. In contrast with most machine/deep learning techniques broadly adopted today, this PhD project proposal has the potential to have an important impact in our understanding of laws in Cosmology, Astrophysics and High Energy Physics, since symbolic techniques result in more interpretative models than possible before.

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).

Coupled tachyonic dark energy: a test in the Euclid era

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1501 - Alberto Rozas-Fernandez

Co-Supervisor: 1795 - Francesco Pace

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

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Astronomy and Astrophysics

Typology: National

The physical model of the Universe includes a component known as dark energy (DE) that accounts for 69% of the energy density in the Universe. Early observations already hinted at the need for such a component, but this became evident in the late 1990´s with the discovery of the accelerated expansion of the Universe. More than twenty years have passed and its nature remains unknown. Various DE models have been proposed but most of them produce very similar expansion rates and cannot be distinguished by measuring the acceleration. The simplest of them has been adopted as the standard model: the LCDM. The best way to discriminate between the various DE models and to test LCDM is through their impact on structure formation. Both the time evolution and spatial distribution of cosmological structures can be probed by weak lensing. ESA´s Euclid mission (operating in 2022-2028) is the main DE survey of our times and will combine weak lensing measurements with galaxy clustering measurements. This will enable it to differenciate between the competing models and hint towards the nature of DE. The period of the proposed project coincides with the final year of preparation of the Euclid mission, of which the candidate’s supervisors are members. The student would become a member too. This preparation includes the scientific exploitation of the future data. The Euclid Theory Working Group has identified a large number of DE, dark matter and modified gravity models as viable alternatives to LCDM that are worth exploring by Euclid. In particular, coupled dark energy models are included in the list. The coupled DE scenario is an attractive approach that alleviates the coincidence problem and has been attracting considerable attention recently. The aim of this tesis is to investigate the coupled tachyon scenario in depth, including conformal and disformal couplings as well as a mixture of both, to be fully comprehensive. These theoretical models must be fully developed to produce unbiased and precise predictions at linear and non-linear level if we want to extract the maximum information from the data. The different coupled tachyon models will be tested first at the linear level against the most recent observational data. Afterwards, we shall explore the mildly non-linear regime. Those preliminary results will then inform the study of the full non-linear regime, to be later tested by Euclid data.

Modified Gravity in Cosmology and 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.

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.

Enhanced Searches with the Pierre Auger Observatory in the Era of Multi-messenger Astrophysics

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 982 - Raul Sarmento

Co-Supervisor: 29 - Ruben Conceição

Co-Supervisor: 26 - Nuno Castro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program: MAP-fis (MAP Doctoral Programme in Physics)

Typology: National

The Pierre Auger Observatory is the experiment most suited to study the highest energy astroparticles and the on-going installation of detector upgrades will improve its measurement capabilities. This thesis proposes to assess the impact of these new tools on reducing the systematics uncertainties, from detector cross-calibrations to air shower phenomenology, on the reconstruction of extensive air showers. The findings will be applied to the development of photon searches in association with fast radio bursts (FRB).

Characterization of liquid argon detectors for next generation neutrino physics

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

Supervisor: 32 - José Maneira

Co-Supervisor: 1729 - Francesco Pietropaolo

Co-Supervisor: 69 - Fernando Barao

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program: PhD in Physics

Typology: National

The question of how neutrinos may be related to the origin of the matter-antimatter asymmetry in the Universe is one of the fundamental goals of Particle Physics today, and the central motivation to accurately measure long baseline neutrino oscillations with the next generation of experiments. The technology of liquid argon time projection chambers (LAr TPCs) allows for massive detectors with excellent tracking and calorimetry -- all crucial capabilities to meet the requirements of the next generation of experiments. In this technique, particles ionize the argon, creating free electrons that drift in an intense electric field and are collected in wire anodes planes, with the measured time providing the drift length. A full characterization of the electric field uniformity and the charge attenuation along the drift are essential to guarantee a precise 3D reconstruction of the neutrino interaction and its energy. This project will be based on the development of calibration and characterization techniques of LAr TPCs with cosmic ray muons, intense UV laser beams, and possibly a dedicated radiation source. It will be focused on the DUNE experiment and its prototype at CERN, ProtoDUNE. New calibration systems will be installed in ProtoDUNE, with the aim of taking data from 2022 onwards. The commissioning and data analysis of ProtoDUNE2 and its calibration systems will be the central part of this work plan, that will conclude with using those results to better estimate the performance of the future DUNE far detector. The candidate will integrate the CERN Neutrino Platform team and will play an active role in the ProtoDUNE2 installation.

Confinement in the complex plane

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 462 - Paulo Silva

Co-Supervisor: 628 - David Dudal

Co-Supervisor: 301 - Orlando Oliveira

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

Degree Institution: Universidade de Coimbra

PhD Program: PhD in Physics

Typology: National

This Phd project is twofold. A first part will concern the study of the photon propagator of compact (lattice) QED in the complex momentum plane. This model exhibits two different phases, a "normal" Coulombic one and a confining one, depending on the strength of the coupling. The confinement mechanism is known to be driven by monopole condensation. As such, this toy gauge model has some interesting resemblance to highly non-perturbative QCD physics, including the role of topological defects. On the other hand, frequently, the confinement of quarks and gluons is assumed to be also encoded in their spectral (analyticity) properties when the momentum is allowed to be complex. We wish to test this conjecture in the compact QED picture, where a good control exists over the phases and recent, high quality, lattice photon propagator data was constructed by the Coimbra group, see https://arxiv.org/pdf/2110.12759.pdf or https://journals.aps.org/prd/abstract/10.1103/PhysRevD.103.094519. Work in progress will include the study of the (temporal) Schwinger function, from which access to the spectral function can also be granted, cf. https://arxiv.org/pdf/2103.11846.pdf. Preliminary yet unpublished results already suggests the sensitivity of the Schwinger function to the phase transition. It is also yet unclear what the influence of adding fermion matter can be, leading to another planned topic of study. A second part is conceptual in nature and concerns the underlying Monte Carlo simulation itself. Recent work of https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.125.121601 introduced a flow-based sampling rooted in Artificial Intelligence research, tested there on 2D QED. One of its advantages is that it avoids “freezing” in the topological sectors (critical slowing down). The dynamics of 4D (compact) QED is richer than in 2D, in particular given the connection between topology and (de)confinement. Applying this newly proposed formalism will be most interesting to explore the precise “phase dynamics” in deeper detail than ever before.

What are the signatures of gravitational waves in non-homogeneous cosmologies?

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 226 - Antonio da Silva

Co-Supervisor: 111 - José Pedro Mimoso

Co-Supervisor: 1861 - Alberto Krone-Martins

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

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Programa doutoral em Física e Astrofísica

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 generally 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. This PhD project will result in a detailed characterization of the properties of the GW signals that may be detected by future experiments, and will assess if a more general class of non-homogeneous and isotropic Lemaître-Tolman-Bondi (LTB) models is able resolve the current cosmological tensions that the Friedmann-Lemaître-Robertson-Walker (FLRW) models and its extensions are currently facing.

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.

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.

High-Precision MIP Timing Detector for the CMS experiment at HL-LHC

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

Supervisor: 1704 - Tahereh Niknejad

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

The work will be developed in the framework of the activities of LIP group in the MTD project. The group is responsible for the design and construction of the BTL readout system. Dedicated ASIC electronics is used in the readout of SiPM arrays coupled to LYSO crystal bars. The readout solution uses the new TOFHIR2 chip developed in the framework of the agreement KN436/EP between LIP and CERN. The microelectronics design of the TOFHIR2 circuits is sub-contracted to the Portuguese company PETsys. A first version of the chip (TOFHIR1) was implemented in the same technology as TOFPET2 (UMC CMOS 110nm). The final version (TOFHIR2) is being developed in TSMC CMOS 130 nm technology, which has increased radiation tolerance. The frontend (FE) system has three types of boards, the FE Board with the TOFHIR2 chips interfacing to LYSO/SiPM modules, the Concentrator Card with optical links to the backend, and the Power Conversion Card, which are integrated in Readout Units. LIP has the responsibility for the design, production and testing of the FE Boards. The first prototype of the Readout Unit based on TOFHIR1 was evaluated in 2020. Measurements with SiPM sensors and laser beams with two complete Readout Units showed excellent results. The first full version of the TOFHIR2 chip was tested. The TOFHIR2 test board was developed and integrated with a standalone DAQ system at the TagusLIP experimental facility. Tests make use of the infrastructure available at TagusLIP, in particular fast lasers, optical benches, radiation sources, cooling systems, electronics equipment and computing infrastructure. Radiation resistance tests are performed at the x-ray irradiation facility at CERN (TID tests) and at the heavy-ion beam in Louvain (SEE tests). A new version of the 32-channel ASIC (TOFHIR2B), implementing an improved version of the challenging circuitry to mitigate the effect of the large SiPM dark count noise due to radiation is now being fabricated. Each ASIC channel contains one pre-amplifier, two post-amplifiers, three leading edge discriminators, two time-to-amplitude converters (TAC), one charge-to-amplitude converter (QAC), one 40MHz 10-bit SAR ADC and local control logic. The input current is replicated into three branches for timing, energy discrimination and charge integration. Pulse filtering is included in the post-amplifiers to mitigate the deterioration of time resolution due to the large DCR induced by radiation (up to 50 GHz) and due to pile-up of LYSO pulse tails. The PhD student is expected to play a major role in the research and development towards the assembly and commissioning of the final detector. The program of work will integrate a broad range of topics in detector physics.

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.

Impacts of modified gravity in high energy astroparticle physics and cosmology

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 466 - Francisco Lobo

Co-Supervisor: 616 - João Rosa

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.

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.

Big Data Processing and Machine Learning for CLOUD/PS215 at CERN

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

Supervisor: 128 - Antonio Amorim

Co-Supervisor: 1957 - Jonathan Duplissy

Co-Supervisor: 1954 - António Tomé

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Physics Engineering

Typology: National

The CLOUD/PS215 experiment at CERN has shown that ions from galactic cosmic rays help to stabilize nucleating clusters against evaporation and, for otherwise weakly bound clusters, that ions can enhance nucleation rates by a factor 10-100, depending on conditions. The CLOUD results on GCR-climate forcing are now informing the IPCC, which writes in its recent climate assessment report, AR6 (Climate Change 2021 - The Physical Science Basis, section 7.3.4.5). The GCR-cloud-climate question is however still not settled. The pristine environment created in the large CLOUD chamber at CERN derives from unique controlled conditions where pure O2 and N2 are mixed with water vapor and several other trace gases unde particle beam and UV illumination. These are drivers to the camera conditions where the trace compounds are nucleating into small aerosol condensation nuclei. The advisors of this proposal combine expertise from the data-collection, significant data processing, and monitoring tasks together with the knowledge on the chemical/nucleation processes occurring in the chamber. Following a very recent line of research for atmospheric observations, we propose to apply and improve machine learning methods to three different problems in the context of the CLOUD experiment: • The control of the camera driving mechanisms for achieving definite conditions like humidity, ozone creation, etc. To reach a given camera state, a non-linear combination of factors must act along extended periods. The work will replace the non-linear “control system” of CLOUD that presently is carried out by user informed trial and adjustment by a trained automatic AI agent. • Automatic identification of new particle formation events (NPF). The non-linear characteristics of the phenomena in the chamber lead to nucleation events that are only detected by humans looking at “banana plots” where the aerosol concentrations for different diameters are plotted over time. We propose looking at these particular plots as images and applying the Region-based Convolution Neural Network method for image recognition to identify and classify these nucleation events. • A significant quantitative way to express the evolution of the aerosol distribution is the aerosol growth rates. These rates are hard to compute from raw instrument data and must be stripped from many factors like wall effects. We propose to train a deep neural network from the observed evolution of aerosol distribution data to provide the growth rates in several conditions. The IA/machine learning methods have a broad impact on society ranging from the banking industry to autonomous driving. The consolidation and broadening of the CLOUD results on aerosol formation have a definite impact on understanding the radiation balance in the atmosphere and any climate change study.

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.

Rare Higgs decays and couplings to quarks

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Co-Supervisor: 1780 - Eliza Melo da Costa

Co-Supervisor: 1777 - Sandro Fonseca de Souza

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

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 2018, both CMS and ATLAS have detected the couplings of the Higgs to the heaviest quarks: the top (ttH) and the bottom (H->bb). Evidence for the muonic decay was also recently achieved by CMS. 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.

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 Engineering at IST (Doutoramento em Engenharia Física Tecnológica 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.

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 Engineering at IST (Doutoramento em Engenharia Física Tecnológica 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, contrary to the SM, 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.

Neutrinos at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Co-Supervisor: 1702 - Alberto Blanco castro

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

Neutrinos are produced abundantly at colliders, still collider neutrinos have yet to be detected. The LHC will deliver the highest energies yet of man-made neutrinos, and their detection will be a milestone. This will be achieved with SND@LHC (the most recent LHC experiment to be proposed and approved). The new detector will be installed in the LHC tunnel, away from the ATLAS collision point and near the beam-line direction. Given its “off-axis” location, the detected neutrinos will originate primarily from heavy flavour decays, which allows to probe heavy flavour production for the first time in a region not acessible to other LHC detectors. The thesis project will involve participation in the installation, commissioning and data taking with the new LHC detector, the development of machine learning tools for signal selection and detector optimization, and the physics analysis of its first data.

Measurements of neutron cross-sections at the NEAR station of the n_TOF spectrometer at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1775 - Pedro Vaz

Co-Supervisor: 1794 - Alberto Mengoni

Host Institution: Centro de Ciências e Tecnologias Nucleares

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: Mixed

Abroad-Institution: CERN

The n_TOF Collaboration gathers 40 laboratories, research centers and Universities in European countries, Japan and Russia and operates the TOF ("Time Of Flight") spectrometer at CERN. Cross-section measurements of neutron induced reactions for different nuclides are being performed since 2001, using the TOF spectrometer. These measurements are of relevance for Nuclear Astrophysics, for the development of innovative and emerging concepts of Nuclear Technology for energy production, , for Fundamental Nuclear Physics, Nuclear Medicine and other applications. The TOF spectrometer is a premier and unique facility worldwide for the measurement, with excellent energy resolution and high accuracy, of neutron-induced reactions, in particular neutron capture and neutron fission cross-sections, for neutrons in a wide energy range, from meV (thermal neutrons) up to hundreds of MeV (fast neutrons). The high instantaneous neutron flux is generated by the CERN/PS proton beam impinging on a lead spallation target. The neutrons are collimated before reaching two experimental areas: EAR-1, located 185 m downstream the target in the forward direction and EAR-2, located 20 m vertically above the target, at 90º from the direction of the incident proton beam. Both experimental areas are equipped with: - Several detection systems for the measurement of the neutron beam intensity and spatial distribution (Silicon and Micromegas detectors) - Various experimental setup, including the samples whose cross-section are to be measured and detection systems positioned around the samples, namely: C6D6 liquid scintillators (in both areas) and a BaF2 calorimeter (in EAR-1) for the detection of photons produced in neutron capture reactions, and Proportional Chambers for the detection of fission fragments from neutron induced fission reactions. During the CERN accelerators shutdown in 2019-2021, a new experimental area was designed and implemented in 2020 and 2021, designated "NEAR station", located near the spallation target, aiming at benefiting from the very high neutron fluxes available, to perform, inter alia: • Measurements of Maxwellian Averaged Capture Cross Sections" (MACS), by activation, of relevance for Nuclear Astrophysics • Fusion related measurements (cross sections) • Measurements of decay rates of long-lived isotopes The workplan for this thesis, includes the participation in the experimental campaigns at CERN to perform the aforementioned measurements, computational studies using Monte Carlo simulations for the design and optimization of experiments and physics analysis activities of experimental data sets.

Arrow of Time: its origin in 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. 


Higgs and top quarks – heavy weights to search new physics at the LHC

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: Doutoramento em Física / PhD in 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.

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.

Perturbations and quasinormal modes of black holes in modified theories of gravity

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1845 - Filipe Moura

Co-Supervisor: 1735 - Jorge Rocha

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

Black holes in the ringdown phase resulting from a black hole collision form a dissipative system which can be described by black hole perturbation theory: they loose energy by emitting gravitational radiation. Those decaying oscillations are called quasinormal modes, and they are given in terms of complex frequencies. The spectrum of black hole quasinormal modes (QNMs) does not depend on what drives the perturbations: it is completely determined by intrinsic physical quantities of the black hole such as mass, charge or spin, and eventually (beyond Einstein gravity) some other parameters of the theory. In spite of their classical origin, QNMs may provide a glimpse into the eventual quantum nature of the black hole. This feature turns QNMs into preferential probes for testing theories of gravity beyond Einstein, since the ringing frequencies represent a universal part of the gravitational wave signals. With the advent of gravitational wave astronomy, therefore, interest in the study of black hole QNMs has raised. Analytical studies of stability and QNM spectra exist mainly for static, stationary black hole solutions. In order to obtain more realistic results, it is necessary to extend these studies to rotating black holes, since astrophysical objects typically have spin. In the context of string theory, this requires obtaining higher order corrections to the Kerr solution in four and higher dimensions. From a purely theoretical point of view, the study of QNMs is also important: according to AdS/CFT, QNMs of an asymptotically AdS black hole or brane are poles of the retarded Green’s function in the dual conformal field theory (CFT) at strong coupling. The latter allows us to describe various properties of strongly coupled quark-gluon plasmas such as transport coefficients, which cannot be studied by traditional perturbative methods of quantum field theory. All studies performed so far in AdS/CFT involving higher-curvature couplings (required by string theory) were restricted to d>4 bulk spacetime dimensions until the recent formulation of Einsteinian cubic gravity. ECG is the most general diffeomorphism-invariant theory of gravity, up to cubic order in curvature, being nontrivial in d=4. It has the same linearized spectrum as Einstein gravity on maximally symmetric backgrounds, and it admits AdS4 black hole solutions with general horizon topology, this way making it possible to extend the study of AdS/CFT with higher order corrections to d=3 nonsupersymmetric CFTs, to which it is dual. There exist many interesting such CFTs with important physical applications. The goal of this thesis is to perform some of these studies and solve some of these open problems, if not in their full generality, at least in some concrete and relevant cases.

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.

Formal and phenomenological studies in the high energy limit of QCD

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1945 - Grigorios Chachamis

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: Programa Doutoral em Física

Typology: National

The high energy limit of Quantum Chromodynamics (QCD) is one of the main fields of study in particle physics. The structure of high energy QCD has new effective degrees of freedom, namely reggeized quarks and gluons, which can form bound states with different quantum numbers among which the best known are the Pomeron[1] and the Odderon [2]. The perturbative hard Pomeron is best described within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) formalism. It corresponds to a bound state of two reggeized gluons and provides the dominant contribution to cross sections at very large colliding energies. The Odderon respectively is a system of three interacting reggeized gluons. Systems with more than three reggeized gluons are also important albeit for more formal studies connected to the nature of scattering amplitudes in the high energy limit. Our formal understanding of bound systems with more than two reggeized gluons is still rather limited whereas the experimental searches are quite complicated since they generally correspond to subleading contributions to cross sections. Moreover, the Pomeron needs to be unitarized and the best candidate is the notion of saturation[3] which accounts for gluon recombination effects. To date, there is no definite claim for a BFKL Pomeron signal at the LHC, however there are very promising channels that still need to be studied at 13 TeV, mainly Mueller-Navelet jets and Mueller-Tang jets. Recently, the TOTEM collaboration at the LHC, together with the D0 collaboration at the former Tevatron collider at Fermilab, have claimed the discovery of the Odderon [4]. In the announcement, it was stated that "This result probes the deepest features of quantum chromodynamics, notably that gluons interact between themselves and that an odd number of gluons are able to be 'colourless', thus shielding the strong interaction".[5] In the light of these experimental developments and the forthcoming experimental analyses focusing on a BFKL Pomeron signal, we urgently need a better theoretical understanding of bound states of reggeized gluons as well as a setup of phenomenological studies that can be confronted directly against the experimental data. [1] L.~N.~Lipatov, Sov. Phys. JETP 63, 904-912 (1986) [2] L. Lukaszuk & B Nicolescu 1973 Nuovo Cimento Lett. 8 405. [3] L.~V.~Gribov, E.~M.~Levin and M.~G.~Ryskin, Phys. Rept. 100, 1-150 (1983) [4] V.~M.~Abazov et al. [TOTEM and D0], Phys. Rev. Lett. 127, no.6, 062003 (2021) [5] https://home.cern/news/news/physics/totem-and-do-collaborations-announce-odderon-discovery [6] J. Bartels, Nucl. Phys. B 175 (1980) 36; J. Kwiecinski and M. Praszalowicz, Phys. Lett. B 94 (1980) 413 [7] I. Balitsky, Nucl. Phys. B463 (1996) 99; Y. V. Kovchegov, Phys. Rev. D60 (1999) 034008 [8] G.~Chachamis and A.~Sabio Vera, Phys. Rev. D 94, no.3, 034019 (2016)

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.

Exploration of hadronic interaction properties with the MARTA Engineering array

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 29 - Ruben Conceição

Co-Supervisor: 982 - Raul Sarmento

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

Nature and arrival direction of cosmic rays at the highest energies can only be inferred indirectly through the analysis of the air shower induced by their interaction with the atmosphere. The understanding of the shower development relies on our knowledge about the hadronic interactions that can occur at energies well above those reachable at accelerators on Earth. Muons, being long-lived particles, carry essential information about these hadronic interactions that rule the shower development. Therefore, their detection at the ground is a crucial tool to understand the physics of extensive air showers and particle interactions at extreme energies. However, the measurement of the highest energy extensive air-showers and in particular of the produced muons poses several challenges as it has to be performed in an outdoor environment, using detectors covering a vast area. The LIP group is leading the MARTA project, which proposes an innovative concept for the muon detection in air-shower experiments. MARTA (Muon Array of RPCs for Tagging Air showers) uses an innovative technique to measure the shower muon component directly. It uses the standard water Cherenkov detector, which is sensitive to all shower components, as an absorber of the electromagnetic shower component. Resistive Plate Chambers, placed below the water tank, with a high segmentation and time resolution, can then be used to measure muons. Several full-scale MARTA prototypes are already installed and taking data in the Pierre Auger Observatory - currently the biggest cosmic ray observatory in the world - situated in Argentina. The MARTA Engineering Array (EA), consisting of seven MARTA stations, is planned to start to be deployed in Auger during 2022. This array will measure the muons on an event-by-event basis. It will collect shower events produced mainly at center-of-mass energies compatible with those reached currently at the Large Hadron Collider, LHC. Hence, MARTA EA data analysis will provide not only strong tests to the shower hadronic physics but also its successful operation would pave the construction of future hybrid cosmic ray experiments.

Axions in plasmas: axion-plasmon polaritons and the active generation of axions

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1958 - Hugo Terças

Host Institution: Instituto de Plasmas e Fusão Nuclear -IPFN

Degree Institution: Universidade de Lisboa

PhD Program: IDPASC - Physics

Typology: National

Axions are hypothetical particles, proposed as an extension of the Standard Model in an attempt to solve the strong CP problem in QCD. The Peccei-Quinn mechanism restores the CP symmetry by promoting the CP angle to a dynamical field - the axion - which is a pseudo-scalar field coupling to the theory. Because of their very long decay time (which is a consequence of the smallness of the CP angle), axions interact very weakly with electromagnetic fields. For that reason, axions are also very good candidates for dark matter, an issue that has attracted a great deal of attention recently. Experimental searches of axion and axion-like particles (ALPs) are based on the conversion between axions and photons. In vacuum, the amplitude of this process is extremely small, rendering detection schemes extremely ineffective. We argue that, in plasmas, the conversion probability increases by several orders of magnitude, as a consequence of the resonance in the axion-plasmon propagator. In this thesis, the candidate will investigate configurations involving plasmas as active media for the production and/or detection of axions. The investigation of some astrophysical and cosmological implications are also expected. The scientific domain of this proposal is extremely active at the international level. The candidate will most likely benefit from interactions with collaborators based on world-class institutions.

Mapping the Dark Side 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 observational evidence for the acceleration of the universe demonstrates that canonical theories of cosmology and particle physics are incomplete. New physics is waiting to be discovered, and forthcoming astrophysical facilities must identify it. The source of acceleration has a low-redshift behaviour akin to a cosmological constant, but current data provides limited information on its high-redshift behaviour and possible interactions. Tackling the dark energy enigma requires extending the redshift range where its behaviour can be mapped. New facilities, such as Euclid, the ELT, and the SKA will enable this, increasing the range and sensitivity of current probes and allowing entirely new tests. This thesis will provide a state-of-the-art exploration of the landscape of physically realistic (as well as observationally viable) dark energy paradigms, with the aim of obtaining optimal discriminating observational tests, in particular between the baseline cosmological constant scenario and dynamical dark energy models. Our ultimate goal is to distinguish between theoretical paradigms, using optimized observational strategies for key medium-term observational facilities in whose preparation, performance optimization and, ultimately, exploitation we will be actively involved. The thesis will focus on Euclid (which the student will join) and broaden to explore synergies and probe combinations with the SKAO and ELT-HIRES.

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.

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 provide templates for robust statistical analysis, implying that none of the current constraints is reliable. This will be a larger problem for next-generation facilities. Moreover, most numerical simulations so far have been performed for the simplest Abelian-Higgs (or Nambu-Goto) model, while realistic cosmic strings will have a non-trivial internal structure, including charges and currents. The scientific goal of the thesis is to fill this gap, continuing the world-leading work, in the supervisor's team, of deploying of a new generation of high-performance, high-scalability GPU-accelerated cosmic defect codes that will match the sensitivity of ongoing and forthcoming observational searches, and using them to develop and calibrate suitable analytic models.

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

Optimization of ELT-HIRES Fundamental Physics Tests

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

Two key fundamental physics science cases for the ELT are the tests of the universality of physical laws (through tests of the stability of dimensionless fundamental constants) and a direct, real-time and model-independent mapping of the expansion rate of the universe (the Sandage test). Each provides a stringent consistency test of the LambdaCDM paradigm and enables unique synergies with traditional cosmological probes, e.g. on the nature of dark energy. The two science cases rely, respectively, on high accuracy and on stability of the wavelength scale, and are therefore science and design drivers for the ELT's high-resolution spectrograph, ELT-HIRES. The ELT first light is foreseen for 2027, and the ELT-HIRES Phase B of construction is about to start. In this thesis the student will be directly involved the ELT-HIRES construction, drawing on ESPRESSO GTO data and other tools to carry out a thorough end-to-end simulation (including instrument effects) of these science cases, and an assessment of the fundamental cosmology impact of ELT-HIRES. For fundamental constants this will rigorously quantify the gains in sensitivity as compared to ESPRESSO. For the redshift drift, for which there is currently no detection, this will identify an ideal measurement strategy, maximizing the statistical significance of the drift detection and complementing existing (model-dependent) constraints from other cosmological probes. Ultimately, the student’s work will be a key contribution to the definition and optimization of the ELT-HIRES fundamental physics observational strategy.

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.

Study of Top Quark Production in Pb+Pb Collisions at the ATLAS-LHC - An experimental and phenomenological approach

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 92 - Helena Santos

Co-Supervisor: 30 - Liliana Apolinário

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Physics

Typology: Mixed

Abroad-Institution: CERN

Ultra-relativistic nucleus-nucleus collisions at the Large Hadron Collider (LHC) provide a unique opportunity to recreate the Quark-Gluon Plasma (QGP) in the laboratory energy frontier. This plasma of quarks and gluons, which is known to behave as a nearly perfect liquid, was the Universe's prevailing state shortly after the Big Bang. The capabilities of ATLAS, namely large acceptance and high granularity calorimeters, afford excellent handles for QGP studies. A primary goal of the Heavy Ion Program of the LHC during Run 3 will be to measure, with unprecedented statistics, the QGP Properties. The expected luminosity increase, combined with the results collected during the previous runs, will unlock novel exclusive channels that so far were out of reach. Among them, top-initiated jets are a novel exploration avenue for QGP time-differential measurements. The goal will be to measure this channel and to explore its phenomenological capabilities to understand the time structure of the QGP.

Neutron background in neutrino detectors

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 15 - Sofia Andringa

Co-Supervisor: 879 - Valentina Lozza

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: FCUL (Universidade de Lisboa)

PhD Program: Doutoramento em Física

Typology: National

Neutrino fundamental properties may be in the origin of the matter anti-matter asymmetry in the Universe and are being searched for in experiments with different detector technologies. Neutrons, produced by cosmic muon spallation or by alpha interaction on detector materials, are an important background for low energy neutrino analyses, such as the search for double beta decay, or the measurements of solar, geo and supernova neutrinos. The aim of this project is to quantify and reduce the main uncertainties for the prediction of neutron production rates, and to measure the corresponding cross-sections in two running neutrino experiments, SNO+ and ProtoDUNE, and in auxiliary dedicated experiments.

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: Doutoramento em Física

Typology: Mixed

Abroad-Institution: CERN

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). 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 at the end of 2021). 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.

Accelerating the ATLAS Trigger system with Graphical Processing Units

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

Supervisor: 55 - Patricia Conde Muino

Co-Supervisor: 1789 - Frank Winklmeier

Co-Supervisor: 1787 - Nuno Roma

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Doutoramento em Engenharia Física

Typology: Mixed

Abroad-Institution: CERN

The LHC is the highest energy particle accelerator ever built. The gigantic ATLAS experiment records proton and ion collisions produced by the LHC to study the most fundamental matter particles and the forces between them. A major upgrade, expected for the years 2025-27, will increase the LHC collision rate up to a factor 7 with respect to the nominal values, to allow acquiring a huge amount of data and pushing the limits of our understanding of Nature. The online event selection system (trigger) is a crucial part of the experiment. It analyses in real time, the 40 MHz event rate, selecting only the potentially interesting collisions for later analysis. After the LHC upgrade, the estimated increase in collision rate, and consequently event size, lead to much longer event reconstruction times, that are not matched by the slower expected growth in computing power at fixed cost. This implies a change in paradigm, increasing parallelism in computer architecture, using concurrency and multithreading and/or hardware accelerators, such as GPUs or FPGAs for handling suitable algorithmic code. The availability of High Performance Computers for offline reconstruction also makes it desirable to have software that can maximally profit from them. The study of hardware accelerators, therefore, is not only interesting for the Trigger system but also for the offline ATLAS reconstruction software. The first ATLAS Trigger GPU prototype was implemented and evaluated in 2015-16 [1]. The LIP Portuguese team was responsible for the calorimeter reconstruction algorithms. The results obtained showed the potential gain but also the limitations of the architecture and implementation done. Recent work indicate that an execution time improvement by a factor 2-5, depending on the event occupancy.

Searching for new particles with astrophysical compact objects

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1476 - Carlos Herdeiro

Co-Supervisor: 1855 - Eugen Radu

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

Dark matter remains a central mystery of modern day science. The elusiveness of dark matter candidates in colliders suggests we further search for its true nature where it was first unveiled - in astrophysics via its gravitational effects. In particular, the new golden age in strong gravity - with the gravitational wave era and remarkable new electromagnetic observations of compact objects - is providing intriguing hints on fuzzy dark matter [1,2]. Such phenomenological studies start from the construction of appropriate compact objects where such fuzzy dark matter plays a key role, both new types of black holes and horizonless compact objects. The goal of this thesis is to go beyond the simplest fuzzy dark matter models, based on abelian fields. A dark sector, like the visible one, may contain non-Abelian fields. The impact of such fields on the phenomenology of compact objects, connecting it to gravitational wave and electromagnetic observations, is the central goal of this thesis. [1] GW190521 as a Merger of Proca Stars: A Potential New Vector Boson of 8.7×10−13  eV J. Calderón Bustillo, N. Sanchis-Gual, A. Torres-Forné, J. A. Font, A. Vajpeyi, R. Smith, C. Herdeiro, E. Radu, S. Leong Phys. Rev. Lett. 126 (2021) 081101 [2] EHT Constraint on the Ultralight Scalar Hair of the M87 Supermassive Black Hole P. V. P. Cunha, C. A. R. Herdeiro, Eugen Radu Universe 5 (2019) 220

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: National

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.

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: National

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.

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.

Vector Boson Scattering processes 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

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.

Search for dark matter at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 1943 - Nicola De Filippis

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 Higgs boson discovered at the LHC in 2012 has properties consistent with those expected in the standard model (SM) and completes it. However, despite the beautiful design and many experimental confirmations, the SM remains an incomplete description of Nature. The SM answers many of the questions about the structure of matter, but there are still several unanswered questions. There is strong astrophysical and cosmological evidence that suggests for the existence of DM and that it makes up approximately 26% of the total mass of the Universe. A number of BSM theories predict the particle origin of DM and several types of particle candidates are proposed. Some of the most popular models propose the DM in the form of stable, electrically neutral, weakly interacting massive particle (WIMPs) with a mass in the range between a few GeV to a few TeV, which opens up the possibility of searches at a particle collider. A search for DM at a collider involves the need to look for a recoil against visible SM particles. Due to the lack of electric charge and weak interaction cross section, the probability that DM particles produced in proton-proton collisions interact with the detectors is expected to be very small, and can be sought via an imbalance in the total momentum transverse to the beams, seen in the detector. Thus, many searches for DM at the LHC involve missing transverse momentum (MET) where a SM particle, X, is produced against the missing transverse momentum, associated with the DM particles escaping the detector, in the so called “MET+X” or “mono-X” final states. In the searches performed at colliders, X may be a jet, a heavy flavor jet, a photon, or a W or Z boson, or a Higgs boson.

Machine Learning and Measurements of Higgs boson properties

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 1943 - Nicola De Filippis

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 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 LHC

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

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].

Analysis of the asymptotic region of asymptotically flat and de-Sitter like spacetimes

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: 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 so-called, 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. [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

Black holes as engines of discovery

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 81 - Vitor Cardoso

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Instituto Superior Técnico (Universidade de Lisboa)

PhD Program: Physics

Typology: National

The newly-born era of gravitational-wave astronomy promises to revolutionize our understanding of strong gravitational fields and of gravitational theory itself. The planned ngEHT and the planned LISA mission, the largest European Space Agency science mission, will enable us to look, with unprecedented experimental sensitivity, at systems in the strong field, non-linear regime. This project will explore how gravitational or electromagnetic waves can encode information about these systems. We will study how gravitational wave emission and propagation is affected by the galactic profile, and we will use observations to map the galactic gravitational potential. The detailed knowledge about gravitational-wave dispersion and polarization can also be used to inform us on fundamental aspects, namely on new fundamental light fields. We will use these features to study and constrain high-energy motivated models of gravity and particle physics in regions of parameter space not accessible by particle accelerators. These questions have been identified as key lines of scientific relevance for the EHT and LISA missions.