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Home page > PhD fellowships > Previous Calls > Proposed PhD subjects 2013-2016 > Implications of the 126 GeV Higgs boson for physics beyond the Standard Model

Implications of the 126 GeV Higgs boson for physics beyond the Standard Model

by Yannis Karyotakis - 25 February 2013

Topics : Implications of the 126 GeV Higgs boson for physics beyond the Standard Model
Proponents : Sabine Kraml
Address : LPSC - 53 rue des Martyrs - 38042 Grenoble Cedex
Phone : + 33 4 76 28 40 52
Contact Email : sabine.kraml@lpsc.in2p3.fr


  Summary Context: The recent discovery of a new particle with mass around 126 GeV and properties consistent with a Standard Model (SM) Higgs boson is a first triumph for the LHC physics program. The next step forward after the discovery is to thoroughly test the SM nature of this Higgs-like signal, determine its role in electroweak (EW) symmetry breaking, and investigate the implications for theories beyond the SM (BSM).
Indeed, while a discovery of the Higgs completes our picture of the SM, the SM still leaves many fundamental questions open. Perhaps the most pressing issue is that the SM does not explain the value of the EW scale itself: Why is the Higgs boson so light when it is predicted to be driven to the scale of Grand Unified Theories, or even the Planck scale, by radiative corrections? Either new physics appears at the EW scale, or the Higgs boson mass is fine tuned at the 10-32 level. So on the one hand we expect physics beyond the SM to explain the Higgs mass, on the other hand the measured mass and signal strengths provide significant constraints on concrete BSM realizations.
Thesis work: The aim of this thesis project is a comprehensive study of the properties of the Higgs-like state based on the published experimental results and of their implications for theories beyond the SM. In particular it is crucial to determine the Higgs couplings to gauge bosons and to fermions relative to SM expectations. Various types of deviations of the Higgs these couplings possible in BSM theories, e.g. the Two-Higgs-Doublet Models (2HDMs), models with singlet-doublet mixing, supersymmetric models such as the Minimal Supersymmetric Standard Model (MSSM) and the Next-to-Minimal Supersymmetric Standard Model (NMSSM), models with extra dimensions such as the Rundall-Sundrum (RS) model, composite Higgs models, etc.. Moreover, new particles present in these models modify the expectations for processes that occur at loop level: gg → H, H →gamma gamma, and H→gammaZ. Fits to experimental measurements and limits will allow to constrain these models and to derive testable predictions (for direct searches for heavier Higgs and other new particles present in these theories, but also for complementary indirect measurements) to distinguish between them. These analyses will also give important input to the analysis design for later phases of the LHC.
The work envisaged here is a continuation and extension of the recent work of S. Kraml and collaborators on this topic. It comprises in part to update and extend the fits started in arXiv:1212.5244 as refined experimental results become available, and to apply the generic fits to specific theories and study the extent to which it is possible to differentiate among models of electroweak symmetry breaking. Moreover, constraints from (and implications for) other sectors, in particular B-physics, but —depending on the theory considered—also cosmology, dark matter searches, proton decay, and/or neutrino physics, can be important and will be taken into account. Last but no least, theoretical uncertainties impacting the fits and model interpretations will be studied in detail.
Requirement : excellent knowledge of QFT as well as of SM and Higgs phenomenology (for the level of a PhD student), very good computational and numerical skills, good command of English in reading, writing and speaking.
We expect the successful candidate to participate in existing collaborations (with colleagues from LAPTh and elsewhere) and closely interact with colleagues from experiment. Active participation in workshops and conferences will be expected as the thesis advances.