Interpreting the 650 GeV and 95 GeV Higgs anomalies in the next-to-two-Higgs-doublet model

Abstract

Recent experimental hints from the Large Hadron Collider (LHC) in di-photon and partially in the $\ddot{I}{„}^{+}\ddot{I}{„}^{-}$ 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 ${\hat{I}}^3{\hat{I}}^{3}b\bar{b}$ 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 ${\hat{I}}^3{\hat{I}}^3$ and $b\bar{b}$ channels). 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 in parameter regions that remain consistent with the relevant experimental $2\ddot{I}ƒ$ intervals for the reported excesses, once all theoretical and experimental constraints are imposed. This interpretation leads to distinctive and testable predictions for the ongoing LHC Run~3 and the forthcoming High-Luminosity LHC (HL-LHC) phase, in particular through correlated rates in the ${\hat{I}}^3{\hat{I}}^{3}b\bar{b}$, $\ddot{I}{„}^{+}\ddot{I}{„}^{-}b\bar{b}$, $b\bar{b}{\hat{I}}^3{\hat{I}}^3$, and ${\hat{I}}^3{\hat{I}}^3\ddot{I}{„}^{+}\ddot{I}{„}^{-}$ final states.

15 pages, 4 figures. Text revised, new figures and references added, version accepted for publication in Physical Review D