Manuel Toharia

Higgs-radion interpretation of the LHC data?

Abstract We explore the parameter choices in the 5-dimensional Randall–Sundrum model with the inclusion of Higgs-radion mixing that can describe current LHC hints for one or more Higgs boson signals.

Higgs Bosons in Warped Space, from the Bulk to the Brane

In the context of warped extra dimensional models with all fields propagating in the bulk, we address the phenomenology of a bulk scalar Higgs boson, and calculate its production cross section at the LHC as well as its tree-level effects on mediating flavor changing neutral currents. We perform the calculations based on two different approaches. First, we compute our predictions analytically by considering all the degrees of freedom emerging from the dimensional reduction [the infinite tower of Kaluza Klein modes (KK)]. In the second approach, we perform our calculations numerically by considering only the effects caused by the first few KK modes, present in the 4-dimensional effective theory. In the case of a Higgs leaking far from the brane, both approaches give the same predictions as the effects of the heavier KK modes decouple. However, as the Higgs boson is pushed toward the TeV brane, the two approaches seem to be equivalent only when one includes heavier and heavier degrees of freedom (which do not seem to decouple). To reconcile these results it is necessary to introduce higher dimension operators which essentially encode the effects of integrating out the heavy KK modes and dress the brane Higgs so that it looks just like a bulk Higgs. However, in the brane Higgs limit, it is not possible to predict if there will be enhancement or suppression in the Higgs production rate since the corrections depend on the phases of higher dimension operators.

Unified flavor symmetry from warped dimensions

a b s t r a c t In a model of warped extra-dimensions with all matter fields in the bulk, we propose a scenario which explains all the masses and mixings of the SM fermions. In this scenario, the same flavor symmetric structure is imposed on all the fermions of the Standard Model (SM), including neutrinos. Due to the exponential sensitivity on bulk fermion masses, a small breaking of this symmetry can be greatly enhanced and produce seemingly un-symmetric hierarchical masses and small mixing angles among the charged fermion zero-modes (SM quarks and charged leptons), thus washing out visible effects of the symmetry. If the Dirac neutrinos are sufficiently localized towards the UV boundary, and the Higgs field leaking into the bulk, the neutrino mass hierarchy and flavor structure will still be largely dominated and reflect the fundamental flavor structure, whereas localization of the quark sector would reflect the effects of the flavor symmetry breaking sector. We explore these features in an example based on which a family permutation symmetry is imposed in both quark and lepton sectors.

Metastable Kinks in the Orbifold

We consider static configurations of bulk scalar fields in extra-dimensional models in which the fifth dimension is an S1/Z2 orbifold. There may exist a finite number of such configurations, with the total number depending on the size of the orbifold interval. We perform a detailed Sturm-Liouville stability analysis that demonstrates that all but the lowest-lying configurations--those with no nodes in the interval--are unstable. We also present a powerful general criterion with which to determine which of these nodeless solutions are stable. The detailed analysis underlying the results presented in this Letter, and applications to specific models, are presented in a comprehensive companion paper [M. Toharia and M. Trodden, arXiv:hep-ph/0708.4008].

Radion Phenomenology with 3 and 4 Generations

We study radion phenomenology in an warped extra-dimension scenario with Standard Model elds 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 avor violating couplings and potentially inuencing 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 nally present the modied decay branching ratios of the radion with an emphasis on the new channels involving avor diagonal and avor violating decays into fourth

Saving the fourth generation Higgs with radion mixing

We study Higgs-radion mixing in a warped extra dimensional model with Standard Model elds 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 and the h), although with a severely restricted parameter space. In particular, the radion interaction scale must be quite low, 1 1:3 TeV. If m 125 GeV, the h state must be heavier (mh > 320). If mh 125 GeV, the state must be quite light or close in mass (m 120 GeV). We also present the modied decay branching ratios of the mixed Higgs-radion states, including avor 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 conrming or further severely constraining this scenario.

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

We study a warped extra-dimension scenario where the Standard Model elds lie in the bulk, with the addition of a fourth family of fermions. We concentrate on the avor structure of the Higgs couplings with fermions in the avor 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 eects

Bulk Higgs with a heavy diphoton signal

We consider scenarios of warped extra-dimensions with all matter fields in the bulk and in which both the hierarchy and the flavor puzzles of the Standard Model are addressed. The simplest extra dimensional extension of the Standard Model Higgs sector, i.e a 5D bulk Higgs doublet, can be a natural and simple explanation to the 750 GeV excess of diphotons hinted at the LHC, with the resonance responsible for the signal being the lightest CP odd excitation coming from the Higgs sector. No new matter content is invoked, the only new ingredient being the presence of (positive) brane localized kinetic terms associated to the 5D bulk Higgs, which allow to reduce the mass of the lightest CP odd Higgs excitation to 750 GeV. Production and decay of this resonance can naturally fit the observed signal when the mass scale of the rest of extradimensional resonances is of order 1 TeV.

Fermion Masses and Mixing in General Warped Extra Dimensional Models

We analyze fermion masses and mixing in a general warped extra dimensional model, where all the Standard Model (SM) fields, including the Higgs, are allowed to propagate in the bulk. In this context, a slightly broken flavor symmetry imposed universally on all fermion fields, without distinction, can generate the full flavor structure of the SM, including quarks, charged leptons and neutrinos. For quarks and charged leptons, the exponential sensitivity of their wave-functions to small flavor breaking effects yield naturally hierarchical masses and mixing as it is usual in warped models with fermions in the bulk. In the neutrino sector, the exponential wave-function factors can be flavor-blind and thus insensitive to the small flavor symmetry breaking effects, directly linking their masses and mixing angles to the flavor symmetric structure of the 5D neutrino Yukawa couplings. The Higgs must be localized in the bulk and the model is naturally more successful in generalized warped scenarios where the metric background solution is different than AdS5. We study these features in two simple frameworks, flavor complimentarily, and flavor democracy, which provide specific predictions and correlations between quarks and leptons, testable as more precise data in the neutrino sector becomes available.

Higgs production in general 5D warped models

We calculate the production rate of the Higgs boson at the LHC in the context of general five-dimensional (5D) warped scenarios with space-time background modified from the usual