The Fermion Mass Hierarchy in Models with Warped Extra Dimensions and a Bulk Higgs

TL;DR

This paper explores how a bulk Higgs in warped extra dimensions can address the fermion mass hierarchy, analyzing phenomenological implications and constraints related to the Higgs VEV profile and electroweak symmetry breaking.

Contribution

It provides a detailed analysis of the Higgs VEV exponent's role in fermion masses and electroweak symmetry breaking within warped extra-dimensional models, highlighting the optimal exponent value and its phenomenological impacts.

Findings

Fermion masses range from 10^{-5} eV to 200 GeV with a Higgs VEV exponent near two.

Flatter Higgs VEVs reduce contributions to the electroweak T parameter.

Constraints from flavor-changing neutral currents are minimized for flatter Higgs VEV profiles.

Abstract

The phenomenological implications of allowing the Higgs to propagate in both AdS${}_5$ and a class of asymptotically AdS spaces are considered. Without tuning, the vacuum expectation value (VEV) of the Higgs is peaked towards the IR tip of the space and hence such a scenario still offers a potential resolution to the gauge-hierarchy problem. When the exponent of the Higgs VEV is approximately two and one assumes order one Yukawa couplings, then the fermion Dirac mass term is found to range from $\sim 10^{-5}$ eV to $\sim 200$ GeV in approximate agreement with the observed fermion masses. However, this result is sensitive to the exponent of the Higgs VEV, which is a free parameter. This paper offers a number of phenomenological and theoretical motivations for considering an exponent of two to be the optimal value. In particular, the exponent is bounded from below by the Breitenlohner-Freedman bound and the requirement that the dual theory resolves the gauge hierarchy problem. While, in the model considered, if the exponent is too large, electroweak symmetry may not be broken. In addition, the holographic method is used to demonstrate, in generality, that the flatter the Higgs VEV, the smaller the contribution to the electroweak $T$ parameter. In addition, the constraints from a large class of gauge mediated and scalar mediated flavour changing neutral currents, will be at minimal values for flatter Higgs VEVs. Some initial steps are taken to investigate the physical scalar degrees of freedom that arise from a mixing between the $W_5/Z_5$ components and the Higgs components.