Radion phenomenology in realistic warped space models

Abstract

We investigate the phenomenology of the Randall-Sundrum (RS) radion in realistic models of electroweak symmetry breaking with bulk gauge and fermion fields, since the radion may turn out to be the lightest particle in such models. We calculate the coupling of the radion in such scenarios to bulk fermion and gauge modes. Special attention needs to be devoted to the coupling to massless gauge fields (photon, gluon), since it is well known that loop effects may be important for these fields. We also present a detailed explanation of these couplings from the conformal field theory interpretation. We then use these couplings to determine the radion branching fractions and discuss some of the discovery potential of the LHC for the radion. We find that the $\ensuremath{\gamma}\ensuremath{\gamma}$ signal is enhanced over most of the range of the radion mass over the $\ensuremath{\gamma}\ensuremath{\gamma}$ signal of a standard model Higgs boson, as long as the RS scale is sufficiently low. However, the signal significance depends strongly on free parameters that characterize the magnitude of bare brane-localized kinetic terms for the massless gauge fields. In the absence of such terms, the signal can be enhanced over the traditional RS1 models (where all standard model fields are localized on the IR brane), but the signal can also be reduced compared to RS1 if the brane-localized terms are sizeable. We also show that for larger radion masses, where the $\ensuremath{\gamma}\ensuremath{\gamma}$ signal is no longer significant, one can use the usual 4 lepton signal to discover the radion.