Implications Of The Higgs Discovery On Physics Beyond The Standard Model

Abstract

In this thesis, we investigate the implications of the LHC Higgs data on different BSM scenarios. Since the data seem to agree with the SM expectations, any nonstandard couplings will be strongly constrained. First we investigate, in a model independent way, the constraints on the nonstandard Higgs couplings with the fermions and the vector bosons in view of high energy unitarity and the measured value of the Higgs to diphoton signal strength. Then we concentrate on a particular BSM scenario, namely, the two Higgs-doublet models (2HDMs). Consistency of the Higgs data with the corresponding SM predictions strongly motivates us to work in the {\em alignment limit}. In this limit, including the informations of Higgs mass and its SM-like nature, we find many new constraints on the nonstandard masses and $\tanβ$. We also study the constraints on the charged scalar mass arising from the $h\to γγ$ signal strength measurements and observe that the charged scalar does not necessarily decouple from the diphoton decay width. We then move on to some particular variants of 2HDMs, known as BGL models, and study the flavor constraints on these models. Here we find that lighter than conventionally allowed nonstandard scalars can successfully negotiate the stringent bounds coming from flavor physics data and can leave unconventional decay signatures that can be used as distinctive features of these models. We also analyze the stability and unitarity constraints in a three Higgs-doublet model (3HDM) with $S_3$ symmetry and find that there must be many more nonstandard particles below 1~TeV. We also observe that the nondecoupling feature of the charged scalar in the context of $h\to γγ$ is not unique to the 2HDMs only, instead it is a general property of the multi doublet extensions of the SM with an exact discrete symmetry.