Bulk Standard Model in the Randall-Sundrum Background

TL;DR

This paper explores embedding the Standard Model in a five-dimensional anti-de Sitter space within the Randall-Sundrum framework, analyzing fermion localization, gauge couplings, and constraints from electroweak data.

Contribution

It extends the Randall-Sundrum model by placing some SM particles in the bulk, studying fermion localization, gauge interactions, and phenomenological constraints.

Findings

Fermion zero modes localize near the boundary with negative tension.

Low-lying KK gauge bosons have significant couplings.

First KK mode must be heavier than 9 TeV based on electroweak data.

Abstract

We discuss issues in an attempt to put the Standard Model (SM) in five-dimensional anti-de Sitter spacetime compactified on $S^1/Z_2$. The recently-proposed approach to the gauge hierarchy problem by using this background geometry, with the SM confined on a boundary, is extended to a situation where (some of) the SM particles reside in the five dimensional bulk. In particular, we find a localization of zero modes of bulk fermions near the boundary with a negative tension. Unlike the compactification with the flat metric, these fermion zero modes couple to Kaluza-Klein (KK) excitations of the SM gauge bosons. Interestingly, only low-lying modes of such KK gauge bosons have non-negligible couplings. Current electroweak precision data give a constraint that the first KK mode be heavier than 9 TeV. We also argue that at least the Higgs field should be confined on the brane to utilize the Randall-Sundrum background as a solution to the gauge hierarchy.