Light (and darkness) from a light hidden Higgs

TL;DR

This paper investigates light Higgs bosons with suppressed fermion couplings, deriving bounds from diphoton data, exploring ways to evade these bounds, and considering implications for models like GM and SGM, including potential signals at the LHC.

Contribution

It provides new bounds on light Higgs bosons in extended sectors using diphoton data and explores mechanisms to evade these constraints, with applications to specific models like GM and SGM.

Findings

Masses below 110 GeV are ruled out if photon coupling is W-boson dominated.

Cancellations between loop contributions can evade existing bounds.

Future LHC diphoton signals from hidden Higgs sectors are possible.

Abstract

We examine light diphoton signals from extended Higgs sectors possessing (approximate) fermiophobia with Standard Model (SM) fermions as well as custodial symmetry. This class of Higgs sectors can be realized in various beyond the SM scenarios and is able to evade many experimental limits, even at light masses, which are otherwise strongly constraining. Below the $WW$ threshold, the most robust probes of the neutral component are di and multi-photon searches. Utilizing the dominant Drell-Yan Higgs pair production mechanism and combining it with updated LHC diphoton data, we derive robust upper bounds on the allowed branching ratio for masses between $45 - 160$ GeV. Furthermore, masses $\lesssim 110$ GeV are ruled out if the coupling to photons is dominated by $W$ boson loops. We then examine two simple ways to evade these bounds via cancellations between different loop contributions or by introducing decays into an invisible sector. This also opens up the possibility of future LHC diphoton signals from a light hidden Higgs sector. As explicit realizations, we consider the Georgi-Machacek (GM) and Supersymmetric GM (SGM) models which contain custodial (degenerate) Higgs bosons with suppressed couplings to SM fermions and, in the SGM model, a (neutralino) LSP. We also breifly examine the recent $\sim 3\sigma$ CMS diphoton excess at $\sim 95$ GeV.