Saving the fourth generation Higgs with radion mixing

We study Higgs-radion mixing in a warped extra dimensional model with Standard Model fields in the bulk, and we include a fourth generation of chiral fermions. The main problem with the fourth generation is that, in the absence of Higgs-radion mixing, it produces a large enhancement in the Higgs production cross-section, now severely constrained by LHC data. We analyze the production and decay rates of the two physical states emerging from the mixing and confront them with present LHC data. We show that the current signals observed can be compatible with the presence of one, or both, of these Higgs-radion mixed states (the $phi$ and the $h$), although with a severely restricted parameter space. In particular, the radion interaction scale must be quite low, Lambda_phi ~ 1-1.3 TeV. If m_phi ~ 125 GeV, the $h$ state must be heavier (m_h>320 GeV). If m_h ~ 125 GeV, the $phi$ state must be quite light or close in mass (m_phi ~ 120 GeV). 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 LHC data. During the present year, a clear picture of this scenario will emerge, either confirming or further severely constraining this scenario.

Radion Phenomenology with 3 and 4 Generations

We study radion phenomenology in an warped extra-dimension scenario with Standard Model fields in the bulk, with and without an additional fourth family of fermions. The radion couplings with the fermions will be generically misaligned with respect to the Standard Model fermion mass matrices, therefore producing some amount of flavor violating couplings and potentially influencing production and decay rates of the radion. Simple analytic expressions for the radion-fermion couplings are obtained with three or four families. We also update and analyze the current experimental limits on radion couplings and on the model parameters, again with both three and four families scenarios. We finally present 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.

Higgs Phenomenology in Warped Extra-Dimensions with a 4th Generation

We study a warped extra-dimension scenario where the Standard Model fields lie in the bulk, with the addition of a fourth family of fermions. We concentrate on the flavor structure of the Higgs couplings with fermions in the flavor anarchy ansatz. Even without a fourth family, these couplings will be generically misaligned with respect to the SM fermion mass matrices. The presence of the fourth family typically enhances the misalignment effects and we show that one should expect them to be highly non-symmetrical 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 $Zto b {bar b}$ or $Z to mu^+ mu^-$. On the other hand, $Delta F=1,2$ processes, mediated by tree-level Higgs exchange, as well as radiative corrections to $b to s gamma$ and $mu to egamma$ put some generic pressure on the allowed size of the flavor violating couplings. But more importantly, these couplings will alter the Higgs decay patterns as well as those of the new fermions, and produce very interesting new signals associated to Higgs phenomenology in high energy colliders. These might become very important indirect signals for these type of models as they would be present even when the KK mass scale is high and no heavy KK particle is discovered.