Prospects for three-body Higgs boson decays into extra light scalars

TL;DR

This paper explores the potential for three-body decays of the Higgs boson into light scalars, revealing scenarios where these decays are significant and could produce detectable six-fermion signatures at colliders.

Contribution

It provides the first detailed analysis of three-body Higgs decays into light scalars within models with a light scalar, identifying conditions and scenarios with observable collider signatures.

Findings

Three-body Higgs decays can be comparable to two-body decays.

Scenarios exist where six-fermion final states are detectable at colliders.

All scenarios are consistent with current experimental constraints.

Abstract

Within models containing a very light scalar particle coupled to the 125 GeV Higgs boson, we present the first detailed study of Higgs decays into three of these light scalars. We determine model-independent conditions which the scalar sector after electroweak symmetry breaking has to satisfy in order for the three-body channel to become relevant. Using a specific model -- the real scalar singlet-extension of the Standard Model (SM) -- we then identify scenarios, where the rates of scalar three-body Higgs decays are comparable to or even exceed those of the well-studied two-body channel. All those scenarios are shown to be compatible with current experimental and theoretical constraints. We finally argue that scalar three-body Higgs decays lead to exciting new collider signatures with six SM fermions in the final state. Calculating the corresponding event rates, we find that e.g. six-muon or six-tau final states may be in reach of dedicated searches at the LHC or ILC experiments.