Electroweak Breaking on a Soft Wall

TL;DR

This paper explores a soft-wall 5D gauge-Higgs model where the IR brane is replaced by a smooth warp factor, leading to new spectra of Kaluza-Klein resonances with less restrictive electroweak constraints.

Contribution

It introduces a soft-wall framework for gauge-Higgs unification, analyzing its impact on resonance spectra and electroweak constraints compared to traditional IR-brane models.

Findings

Resonances can follow linear Regge trajectories or form a continuum.

Electroweak constraints are less severe, allowing lighter resonances.

The lightest resonance can be as low as 2 TeV, with continuum starting below 1 TeV.

Abstract

We extend the 5D gauge-higgs scenario to the soft-wall framework where the IR brane is replaced by a smoothly decaying warp factor. The electroweak symmetry of the Standard Model is embedded in a larger symmetry group whose gauge bosons propagate in the bulk of a warped fifth dimension. This gauge symmetry is partly broken by UV boundary conditions and by a condensate of a bulk scalar field. The Higgs boson lives partly in the 5th component of the gauge field, and partly in the the bulk scalar. The Higgs potential is not UV sensitive if the condensate vanishes fast enough in the UV region. The soft-wall realization opens new possibilities for the spectrum and the couplings of the Kaluza-Klein resonances. We study two particular soft-wall backgrounds: one with resonances whose masses follow the linear Regge trajectory, and another with a continuum above a mass gap. We find that constraints on the Kaluza-Klein scale from electroweak precision tests are less severe than in analogous models with the IR brane. For the linear spectrum the typical constraint on the lightest resonance mass is 2 TeV, while the continuum is allowed to start below 1 TeV.