Radion Couplings to Bulk Fields in the Randall-Sundrum Model

TL;DR

This work analyzes how placing SM gauge bosons and fermions in the RS bulk (with the Higgs on the TeV brane) alters the radion's couplings relative to the traditional brane-confined scenario. The author derives the bulk-induced radion interactions from the 5D metric and stress-energy tensor, showing that bulk fermion zero-modes do not couple to the radion at tree level, while bulk gauge bosons acquire new tree-level terms that enhance radion decays to gg by roughly 40–50% and can drastically alter γγ decays, depending on the radion mass. The results indicate that, apart from gg and γγ channels, most radion decay modes are similar between bulk and brane realizations, but the modified branching fractions could provide collider-accessible distinctions between the two setups. Radion–Higgs mixing is also considered, revealing ξ-dependent shifts in couplings that can further affect Higgs and radion phenomenology, reinforcing the potential to probe SM field localization in the RS framework at colliders.

Abstract

The radion may be the lightest new state present in the Randall-Sundrum(RS) model. We examine the couplings of the radion to the Standard Model(SM) fields in the scenario where they propagate in the bulk and expand into Kaluza-Klein towers. These couplings are then contrasted with those of the more familiar case where the SM fields are confined to the TeV brane. We find that the couplings of the radion to both $gg$ and $γγ$ can be significantly different in these two cases. Implications for radion collider phenomenology are discussed.