Interpreting the 650 GeV and 95 GeV Higgs Anomalies in the N2HDM

Abstract: Recent experimental hints from the Large Hadron Collider (LHC) in di-photon and partially in the $\tau^+\tau^-$ final states suggest the possible existence of an additional Higgs boson with a mass around 95 GeV. Interestingly, these observations are consistent with earlier results from the Large Electron-Positron (LEP) collider, which pointed to an excess in $b\bar b$ final states within a similar mass range. Additionally, CMS has observed an excess in the $\gamma\gamma b\bar{b}$ final state, indicating a possible resonance near 650 GeV decaying into a pair of SM-like Higgs bosons or into a SM-like Higgs boson accompanied by a lighter scalar with mass near 95 GeV. In this work, we investigate whether these anomalies can be simultaneously explained within the Next-to-2-Higgs-Doublet Model (N2HDM), an extension of the Standard Model (SM) scalar sector featuring two complex Higgs doublets and an additional real singlet. Assuming the existence of a CP-even Higgs state compatible with the 95 GeV excesses (restricted to the $\gamma\gamma$ and $b\bar b$ channels), we analyse the Type-II and Type-Y Yukawa structures, taking the observed 650 GeV resonance to be a CP-even Higgs state. An extensive parameter scan is performed, incorporating the latest constraints. Our results show that a heavy CP-even Higgs resonance around 650 GeV, produced predominantly via gluon-gluon fusion and subsequently decaying into a 125 GeV Higgs boson together with another scalar at approximately 95 GeV, can be simultaneously accommodated within both the N2HDM Type-II and Type-Y frameworks at a significance level of 2$\sigma$. This interpretation leads to distinctive and testable predictions from the N2HDM for the ongoing LHC Run-3 and the forthcoming High-Luminosity LHC (HL-LHC) phase.