A 96 GeV Higgs Boson in the 2HDM plus Singlet

TL;DR

This paper interprets a potential 96 GeV Higgs signal as arising from a 2HDM plus singlet model, fitting existing excesses and constraints, and discusses future collider prospects for detailed measurements.

Contribution

It demonstrates that both 2HDM plus singlet models can simultaneously explain the observed excesses and remain consistent with current Higgs data and bounds.

Findings

Both models fit the 96 GeV excesses well.

The second lightest Higgs aligns with the 125 GeV Higgs measurements.

Future colliders like the ILC can further analyze this Higgs sector.

Abstract

We discuss a $\sim 3\,\sigma$ signal (local) in the light Higgs-boson search in the diphoton decay mode at $\sim 96$ GeV as reported by CMS, together with a $\sim 2\,\sigma$ excess (local) in the $b \bar b$ final state at LEP in the same mass range. We interpret this possible signal as a Higgs boson in the 2 Higgs Doublet Model type II with an additional Higgs singlet, which can be either complex (2HDMS) or real (N2HDM). We find that the lightest CP-even Higgs boson of the two models can equally yield a perfect fit to both excesses simultaneously, while the second lightest state is in full agreement with the Higgs-boson measurements at $125$ GeV, and the full Higgs-boson sector is in agreement with all Higgs exclusion bounds from LEP, the Tevatron and the LHC as well as other theoretical and experimental constraints. We derive bounds on the 2HDMS and N2HDM Higgs sectors from a fit to both excesses and describe how this signal can be further analyzed at future $e^+e^-$ colliders, such as the ILC. We analyze in detail the anticipated precision of the coupling measurements of the $96$ GeV Higgs boson at the ILC. We find that these Higgs-boson measurements at the LHC and the ILC cannot distinguish between the two Higgs-sector realizations.