Bulk Stabilization, the Extra-Dimensional Higgs Portal and Missing Energy in Higgs Events

TL;DR

This paper explores how extra-dimensional Higgs portals influence Higgs properties, leading to potential collider signals and astrophysical effects, with implications for vacuum stability and new physics detection.

Contribution

It introduces a detailed analysis of Higgs-bulk coupling effects in extra dimensions, highlighting observable collider signatures and astrophysical constraints.

Findings

Higgs-bulk mixing causes invisible Higgs decays and missing-energy signals.

Astrophysical bounds complement collider constraints on extra-dimensional models.

Modifications to Higgs mass-coupling relations affect vacuum stability analysis.

Abstract

To solve the hierarchy problem, extra-dimensional models must explain why the new dimensions stabilize to the right size, and the known mechanisms for doing so require bulk scalars that couple to the branes. Because of these couplings the energetics of dimensional stabilization competes with the energetics of the Higgs vacuum, with potentially observable effects. These effects are particularly strong for one or two extra dimensions because the bulk-Higgs couplings can then be super-renormalizable or dimensionless. Experimental reach for such extra-dimensional Higgs `portals' are stronger than for gravitational couplings because they are less suppressed at low-energies. We compute how Higgs-bulk coupling through such a portal with two extra dimensions back-reacts onto properties of the Higgs boson. When the KK mass is smaller than the Higgs mass, mixing with KK modes results in an invisible Higgs decay width, missing-energy signals at high-energy colliders, and new mechanisms of energy loss in stars and supernovae. Astrophysical bounds turn out to be complementary to collider measurements, with observable LHC signals allowed by existing constraints. We comment on the changes to the Higgs mass-coupling relationship caused by Higgs-bulk mixing, and how the resulting modifications to the running of Higgs couplings alter vacuum-stability and triviality bounds.