Exploring extensions of the scalar sector of the standard model

Abstract

The Standard Model is one of the most successful theories which describes strong, weak and electromagnetic forces and interactions between the elementary particles. The scalar boson has been found at the Large Hadron Collider (LHC) on 4th July 2012 that has con rmed the Higgs mechanism. Although, the properties of this scalar are consistent with the Higgs as predicted by the standard model (SM), the experimental data still allow an extension of the scalar sector. The standard model fails to explain few physical phenomena in Nature, for example, the presence of dark matter, existence of massive neutrino, the observed matter-antimatter asymmetry, in ation of the Universe, etc. These phenomena indicate the presence of new physics beyond the standard model. In this thesis, various extensions of the scalar sector have been considered comprising of di erent SU(2)L multiplets. The main purpose for writing this thesis is to explore properties of these new scalars using the weak vector boson scattering processes and from the (meta)stability of the scalar potential. If the extended scalar sector participates in the electroweak symmetry breaking then these extra scalars need to couple with the known standard model particles. In this work, it has been shown that the vector boson scattering involving scalar boson exchanges provide a complimentary way to direct search methods to probe into the scalar sector. As di erent extended scalar sectors have similar types of scalar elds, e.g., an extra CP-even Higgs, charged Higgs etc., these new physics models can give rise to the similar types of experimental signatures. In this work, it has been shown that it is possible to distinguish between such models at various vector boson scattering processes by looking at the resonances. Also, the shapes of the resonances can provide further insight to the relevant parameter space of these models. As in the SM, the electroweak vacuum is metastable, it is important to explore ifan extended scalar has an answer in its reserve. As the scalar weakly interacting massive scalar particles protected by Z2 symmetry can serve as viable dark matter candidates, it is interesting to explore if they help prolong the lifetime of the Universe. The e ective Higgs potential gets modi ed in the presence of these new extra scalars, improving the stability of electroweak vacuum. Such an exercise has been undertaken in various kinds of extended scalar sectors. In order to show the explicit dependence of the electroweak stability on di erent parameters of these extended sectors, various kinds of phase diagrams have been presented. Graphical demonstrations have been provided to illustrate how the confidence level, at which stability of electroweak vacuum is excluded, depends on such new physics parameters. This study will help to estimate the lifetime of the electroweak vacuum, especially if it still remains in the metastable state in the extended scalar sectors.