Abstract

In this thesis we study models Beyond the Standard Model including Left-Right Supersymmetric Model and Warped Extra Dimensional Models with a Fourth Generation.

First, we revisit the Higgs sector of Left-Right Supersymmetric Model by studying the scalar potential in a version of the model in which the minimum is the charge and R-parity conserving vacuum state, and there are no additional non-renormalizable terms in the Lagrangian. We try to find a parameter space predicting at least one light doubly-charged Higgs boson, light neutral avor-conserving Higgs bosons. The Flavor-violating ones are heavy, and within the limits from Delta F = 1,2 mixings. The parameter space for such Higgs masses and mixings is very restrictive, thus making the model more predictive.

Subsequently, we study warped extra-dimensional scenarios in the presence of a fourth family of fermions and with the fermion fields lying in the bulk. We concentrate on the flavor structure of the Higgs couplings with fermions in the flavor anarchy ansatz. The occupancy of the fourth family in the model typically enhances the misalignment effects and we show that one should expect them to be highly nonsymmetrical in the (34) inter-generational mixing. The radiative corrections from the new fermions and their flavor violating couplings to the Higgs affect negligibly known experimental precision measurements such as the oblique parameters and Z -> b \bar{b}or Z -> mu^ +mu^-. On the other hand, Delta F = 1, 2 processes, mediated by tree-level Higgs exchange, as well as radiative corrections to b -> s gamma and mu to e gamma put some pressure on the allowed size of the flavor violating couplings. These couplings produce distinguishable signals in high energy colliders as they alter the Higgs decay patterns as well as those of the new fermions. These signals might become very important indirect signals for these type of models as they would be present even when the Kaluza-Klein mass scale is high and no heavy Kaluza-Klein particle is discovered.

Afterwards, we focus on the radion phenomenology in the same scenario with and without an additional fourth family of fermions. The radion couplings with the fermions are also generically misaligned with respect to the Standard Model fermion mass matrices as in the Higgs case, therefore producing some amount of flavor violating couplings and potentially influencing production and decay rates of the radion. We present simple analytic expressions for the radion-fermion couplings with three or four families. We also update and analyze the current experimental limits on radion couplings and on the model parameters. The modified decay branching ratios of the radion with an emphasis on the new channels involving flavor diagonal and flavor violating decays into fourth generation quarks and leptons are provided.

Finally, we study the Higgs-radion mixing in a warped extra dimensional model in the same scenario. The fourth generation Higgs is now severely constrained by Large Hadron Collider data due to the large enhancement in the Higgs production cross-section in the absence of Higgs-radion mixing. We analyze the production and decay rates of the two physical states emerging from the mixing and confront them with present Large Hadron Collider data. We show that the current signals observed can be compatible with the presence of one, or both, of these Higgs-radion mixed states, although with a severely restricted parameter space. We also present the modified decay branching ratios of the mixed Higgs-radion states, including flavor violating decays into fourth generation quarks and leptons. The windows of allowed parameter space obtained are very sensitive to the increased precision of upcoming Large Hadron Collider data. During the present year, a clear picture of this scenario will emerge, either confirming or further severely constraining this scenario.