(Dys)Zphilia or a custodial breaking Higgs at the LHC

TL;DR

This paper investigates potential custodial symmetry breaking in Higgs couplings at the LHC, fitting experimental data to identify possible deviations and discussing future measurements to resolve ambiguities.

Contribution

It introduces a generic Higgs parameterization allowing custodial symmetry breaking and analyzes LHC data to identify degenerate best-fit points related to Higgs couplings.

Findings

Two degenerate best-fit points, Zphilic and dysZphilic, fit the data.

Enhanced ZZ channel can be explained by custodial breaking couplings.

Future collider measurements could distinguish between the scenarios.

Abstract

Electroweak precision measurements established that custodial symmetry is preserved to a good accuracy in the gauge sector after electroweak symmetry breaking. However, recent LHC results might be interpreted as pointing towards Higgs couplings that do not respect such symmetry. Motivated by this possibility, we reconsider the presence of an explicitly custodial breaking coupling in a generic Higgs parameterization. After briefly commenting on the large UV sensitivity of the T parameter to such a coupling, we perform a fit to results of Higgs searches at LHC and Tevatron, and find that the apparent enhancement of the ZZ channel with respect to WW can be accommodated. Two degenerate best-fit points are present, which we label `Zphilic' and `dysZphilic' depending on the sign of the hZZ coupling. Finally we highlight some measurements at future linear colliders that may remove such degeneracy.