The radion, a scalar particle associated with the radius of a compact warped extra dimension, may be the lightest new particle in this class of models. Its couplings to SM particles are proportional to the their masses, similar to the usual Higgs boson, but suppressed by a scale Λr, the radion vacuum expectation value. The main differences are the coupling to massless gauge bosons that receives contribution from the trace anomaly of the energy-momentum tensor due to the the nonvanishing β functions and the mixing with the Higgs boson arising from a nonminimal coupling to gravity parametrized by a dimensionless coefficient ξ. In particular, these differences can result in significant modifications of the radion phenomenology. We use current LHC data on Higgs searches to find exclusion regions on the parameters of a radion model, Λr, ξ and the radion mass mr. We find that, even for low values of Λr, the radion can still have a mass in the region where the Standard Model Higgs has been excluded, for a narrow range of values for the mixing parameter. Some signals at the LHC for this scenario are discussed. We also find that it is possible to hide the Higgs boson in the current searches in this model, due to a suppression of its couplings.

Abstract:We investigate the issue of anomalous contribution to the T parameter and to Flavor Changing Neutral Currents in models with two Higgs doublets arising as composite pseudo Nambu-Goldstone modes. The non linear Lagrangians of several models are explicitly derived and the anomalous contributions to T are identified. The breaking patterns SU(5) → SU(4) × U(1) and SU(5) → SU(4), are analyzed first and we show how anomalous contributions to T arise in both models. Apart from that, the embedding of the Standard Model fermions in a 10 of SU(5) avoids at the same time large corrections to the Zbb coupling and Flavor Changing Neutral Current transitions. Finally, we propose a model based on the breaking SO(9)/SO(8) that is free from anomalous contributions to T and in which the problems of the Zbb coupling and of Flavor Changing Neutral Currents can be simultaneously solved.

We propose a new observable designed to probe CP-violating coupling of the Higgs boson to W bosons using associated Higgs production. We define an asymmetry that measures the number of leptons from W decays relative to the plane defined by the beam line and the Higgs boson momentum. The orientation of that plane is determined by the direction of fermions in the initial state, so that in a proton-proton collider it requires rapidity cuts that preferentially select quarks over antiquarks.

In this letter we study the process of gluon fusion into a pair of Higgs bosons in a model with one universal extra dimension. We find that the contributions from the extra top quark Kaluza-Klein excitations lead to a Higgs pair production cross section at the LHC that can be significantly altered compared to the Standard Model value for small values of the compactification scale.

Models of warped extra dimensions with custodial symmetry usually predict the existence of a light Kaluza-Klein fermion arising as a partner of the right-handed top quark, sometimes called light custodians which we will denotebR. The production of these particles at the LHC can give rise to multi-W events which could be observed in same-sign dilepton channels, but its mass reconstruction is challenging. In this letter we study the possibility of finding a signal for the pair production of this new particle at the LHC focusing on a rarer, but cleaner decay mode of a light custodian into a Z boson and a b-quark. In this mode it would be possible to reconstruct the light custodian mass. In addition to the dominant standard model QCD production processes, we include the contribution of a Kaluza-Klein gluon first mode. We find that thebR stands out from the background as a peak in the bZ invariant mass. However, when taking into account only the electronic and muonic decay modes of the Z boson and b−tagging efficiencies, the LHC will have access only to the very light range of masses, mb = O(500) GeV.

Metastable charged particles produced at the LHC can decay in the quiescent period between beam crossing in the detector leading to spectacular signals. In this paper we consider augmenting the Standard Model with gluino, Higgsino and wino-like particles without invoking supersymmetry. Proton stability is ensured by imposing a discrete $Z_6$ parity that fixes their possible interaction and makes them metastable in a large portion of the parameter space. We investigate the possibility of employing these fields to improve gauge coupling unification, explain dark matter, generate neutrino mass and cancel flavor anomalies. We find that the masses of these fields, controlled by the flavor anomaly relations, make them visible at the LHC.Comment: 12 pages, 1 figure. Matches version published in Phys Lett