Intensity-Frontier Signals of Warped Extra Dimensions

Abstract

Can warped extra dimensions first appear at the intensity frontier rather than as TeV-scale resonances at colliders? We explore this possibility in extended warped models in which gravity propagates to a deep infrared region with warped scale $Λ_{\rm IR}\sim \mathcal{O}({\rm MeV})$, producing a densely spaced Kaluza-Klein (KK) graviton tower. We develop a benchmark photon-portal realization in which a visible vector sector reaches an intermediate GeV-scale brane, while the Higgs sector remains associated with a higher warped scale. The resulting graviton-photon couplings are controlled by wave-function overlap in the extra dimension, so the production rate is not governed simply by an independent mass and coupling as in conventional light-mediator simplified models. Instead, GeV-scale photons in beam-dump environments can preferentially produce heavier KK gravitons whose profiles probe the intermediate brane, after which the excited modes cascade down the tower. If decays into radion-like states are kinematically closed for the terminal mode, the lightest accessible KK graviton can be long-lived and decay visibly into a pair of photons. This leads to a distinctive intensity-frontier signature: heavy-mode production, intratower showering, and macroscopic electromagnetic decays. We present the model ingredients, derive the relevant overlap-controlled couplings, characterize the generic production and decay phenomenology, and discuss the theoretical and precision constraints on this class of low-scale warped scenarios.