Thesis

Phenomenology of Standard Model extensions with enlarged scalar sectors

• Call:

  IDPASC Portugal - PHD Programme 2019

• Academic Year:

  2019 / 2020

• Domain:

  Theoretical Particle Physics

• Supervisor:

  Pedro Ferreira

• Co-Supervisor:

• Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Host Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Abstract:

  The Standard Model of particle physics is a very successful theory, but leaves many questions unanswered, such as the nature of Dark Matter and the matter-antimatter asymmetry observedinthe universe. Models with enlarged scalar sectors (in which more than one Higgs boson particle are predicted) provide answers for some of those questions. One such model is the Two Higgs Doublet model, first proposed in 1973, but which is currently being thoroughly analysed thanks to the existence of experimental data from LHC, which is already constraining enormously the available parameter space of the theory. Phenomenological studies of the model (that is, prediciting values for observables to be tested at the LHC) necessitates a thorough theoretical understanding of the model, and deepening of procedures which have thus far been applied but, with the increasing precision emerging frm experiments, need to be updated and refined. One such procedure is the relationship between the Higgs potential parameters (in the most used version of the 2HDM, eight of them) and physical observables (such as the five physical masses and the angles alpha and beta which characterize all couplings of scalars to fermions and gauge bosons). Thus far, most phenomenological analyses use tree-level relationships to obtain the potential's parameters from physical quantities, but one-loop precision is beginning to be necessary. The thesis will therefore concentrate on obtaining the one-loop expressions for the scalar masses - and other observables - and from them extracting the quadratic and quartic couplings of the 2HDM scalar potential, confronting these results with those obtained from the tree-level approach. Then, those potential parameters will be confronted with theoretical requirements that the potential needs to obey - namely, that the potential be bounded from below (it must have a stable minimum) and obey unitarity (total probability of a given process cannot exceed unity). To begin a simple version of the 2HDM will be analysed - the Inert Model, which provides dark matter candidates. The re-analyses of all dark matter observable constraints will then be undertaken. The Inert Model is currently very contrained by experimental data, and a possible reason for it is the use of tree-level relations between the potential and physical observables. With what is learned from the Inert case, the student will then progress to the full 2HDM. Further models (such as extensions of the Standard Model with extra singlets, complex or real, or a number of doublets eqal to three) will then also be considered. The calculations necessary will be a mix of paper-and-pencyl deductions (to obtain the theoretical expressions from literature, or re-calculate them) and computer numerical scans to probe the models' parameter space. The use of internationally available and renowned computer codes for particle physics phenomenology (such as the codes ScannerS for analyses of the scalar sector, Madgraph and SUSHI for computation of cross sections, MICROmegas for dark matter analyses) will be a crucial part of the work of the PhD student. Attendance of international Schools for PhD students and presentation of results in international conferences will be encouraged and expected. The project will include an ongoing collaboration with experimental physicists.