Phenomenology of Infrared Smooth Warped Extra Dimensions

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We study the effect of the infrared (IR) geometry on the phenomenology of warped extra dimensions with gauge and fermion fields in the bulk. We focus in particular on a "mass gap" metric which is AdS in the ultraviolet, but asymptotes to flat space in the IR, breaking conformal symmetry. These metrics can be dialed to approximate well the geometries arising in certain classes of warped string compactifications. We find, similar to our earlier results on the Kaluza-Klein (KK) graviton, that these metrics give rise to phenomenologically significant shifts in the separation of KK gauge modes in the mass spectrum (up to factors of 2) and their couplings to IR localized fields (up to factors of 5-10 increase). We find that, despite shifts in the spectra, the constraint mₖK > 3 TeV from S remains robust in the class of 5-d mass gap metrics, and that the change to T is not significant enough to remove the need for custodial symmetry.