Thesis

Phenomenological implications of Little Higgs models.

• Call:

  IDPASC Portugal - PHD Programme 2019

• Academic Year:

  2019 / 2020

• Domains:

  Theoretical Particle Physics | Experimental Particle Physics

• Supervisor:

  Jose Santiago

• Co-Supervisor:

  Nuno Castro

• Institution:

  Universidade do Minho

• Host Institution:

  LIP and Universidad de Granada

• Abstract:

  The discovery of the Higgs boson by the ATLAS and CMS collaborations in 2012 represented the experimental confirmation of the Standard Model of particle physics. Since then, the main emphasis of the particle physics community has shifted towards the search of physics beyond the Standard Model (BSM). Supersymmetry and composite Higgs models are the two leading candidates for a natural theory of BSM physics. Among the latter, Little Higgs (LH) models with T-parity are particularly well motivated as the ingenious idea of collective symmetry breaking together with T-parity guarantee the calculability of the models at one loop order. Due to their rich spectrum, LH models can be efficiently probed in a variety of experimental directions, including LHC and future particle colliders, flavor physics and astrophysical and cosmological experiments. Many of the phenomenological implications of LH models have been studied in the past. However most of these studies were done before the LHC actually started and thefore have to be updated using the real LHC data that we have at our disposal now. Furthermore little effort has been performed so far in drawing a comprehensive picture of LH models and their phenomenology. Usually the phenomenological studies focus on one particular aspect without taking full advantage of other experimental probes that can be complementary to the ones under consideration. The point of view adopted in this thesis is the opposite. We will try to build a comprehensive view of the status of LH models by considering all possible experimental and theoretical tests of the models with emphasis on their complementarity. In order to do that we will focus on the Littlest Higgs model with T-parity (LHT). This model is strongly constrained by flavor experiments, constraints that can only be evaded currently by means of fine-tuning. Our first step will consist of studying possible flavor symmetry structures that naturally protect the model for these very stringent constraints. Once we have a successful theory of flavor for the LHT we will study its implications in the vacuum structure of the model. We will then proceed to study its main phenomenological signatures in LHC and dark matter searches. This will be done in a coordinated way, taking into account simultaneously the constraints from both collider and astrophysical/cosmological probes. A more detailed account of this working plan is as follows: - Flavor models of LHT: We will consider different flavor symmetries that protect the LHT from large flavor violation. We will start with the lepton sector and extend it later to the quark sector of the model. Ideally these flavor symmetries will also predict the observed structure of fermion masses and mixing angles in the Standard Model. - Vacuum structure of the model. Once we have established a successful theory of flavor for the LHT we will study its implications in the Coleman-Weinberg potential giving mass (and vacuum expectation value) to the scalars in the theory. This in turn induces correlations among the different particles in the spectrum. - Once the spectrum of the model is fixed by the flavor symmetries we will proceed to study its phenomenological implications in collider and astrophysical and cosmological experiments. In order to do that we will start with general purpose phenomenological studies based on parameterizations of LHC experimental searches. We will analyze the current results and select the most promising experimental searches to constrain the model. We will then consider in detail these searches and their implications on the spectrum of the model, always correlating these results with the ones from cosmological and astrophysical probes, in particular with the successful explanation of the observed dark matter relic abundance in the context of the LHT. - Design of new analyses and extrapolation to future experiments. In a final step we will propose new experimental searches, both at the LHC and at future colliders, that increase the sensitivity to the LHT. We will use these optimized analyses to estimate the reach of future and planned collider experiments as well as other possible astrophysical and cosmological probes, like gravitational waves. This working plan will be done in the Universities of Minho (Portugal) and Granada (Spain), profiting from the expertise on theoretical and experimental high energy physics of the two groups (LIP and CAFPE).