The “96 GeV excess” at the LHC

The CMS collaboration reported an intriguing [Formula: see text] (local) excess at 96 GeV in the light Higgs-boson search in the diphoton decay mode. This mass coincides with a [Formula: see text] (local) excess in the [Formula: see text] final state at LEP. We briefly review the proposed combined interpretations for the two excesses. In more detail, we review the interpretation of this possible signal as the lightest Higgs boson in the 2 Higgs Doublet Model with an additional real Higgs singlet (N2HDM). We show which channels have the best prospects for the discovery of additional Higgs bosons at the upcoming Run 3 of the LHC.

A 96 GeV Higgs boson in the N2HDM

We discuss a $$\sim 3\,\sigma $$∼3σ signal (local) in the light Higgs-boson search in the diphoton decay mode at $$\sim 96 \,\, \mathrm {GeV}$$∼96GeV as reported by CMS, together with a $$\sim 2\,\sigma $$∼2σ excess (local) in the $$b {{\bar{b}}}$$bb¯ final state at LEP in the same mass range. We interpret this possible signal as a Higgs boson in the 2 Higgs Doublet Model with an additional real Higgs singlet (N2HDM). We find that the lightest Higgs boson of the N2HDM can perfectly fit both excesses simultaneously, while the second lightest state is in full agreement with the Higgs-boson measurements at $$125 \,\, \mathrm {GeV}$$125GeV, 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 show that only the N2HDM type II and IV can fit both the LEP excess and the CMS excess with a large ggF production component at $$\sim 96 \,\, \mathrm {GeV}$$∼96GeV. We derive bounds on the N2HDM Higgs sector from a fit to both excesses and describe how this signal can be further analyzed at the LHC and at future $$e^+e^-$$e+e- colliders, such as the ILC.