Is the radion a bulk Higgs doublet?

TL;DR

This paper critically examines a Randall-Sundrum model where the radion is a bulk Higgs doublet, concluding that such a model is incompatible with current LHC data and scalar sector extensions.

Contribution

The paper demonstrates that extending the bulk Higgs doublet model with fermions or additional scalars does not resolve conflicts with experimental data, ruling out the radion as a bulk doublet.

Findings

LHC data rules out the original GBS model.

Extending the model with bulk fermions does not fix the conflict.

Adding a second Higgs scalar leads to a zero mass scalar, which is phenomenologically unacceptable.

Abstract

In 2013, Geller, Bar-Shalom and Soni (GBS) proposed a Randall-Sundrum model with a bulk SU(2) doublet. They found that the doublet could both stabilize the extra dimension and break the electroweak symmetry; the radion and the Higgs boson were then one and the same. This alternative to the Goldberger-Wise mechanism contained enhanced Higgs couplings to gluons and photons, but at the time of the GBS paper, these couplings were phenomenologically acceptable. We note that updated results from the LHC rule out the model as presented. One can expand the parameter space by extending the model to include bulk fermions. We do so, and show that for any choice of parameters, the model remains in conflict with LHC data. We then extend the scalar sector to a two Higgs model, and show that the model contains a phenomenologically unacceptable zero mass scalar. This property will likely apply to all extensions to the scalar sector, and thus we conclude that the radion cannot be part of a bulk doublet.