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

TL;DR

This paper explores whether recent Higgs anomalies at 95 GeV and 650 GeV can be explained within the Next-to-2-Higgs-Doublet Model, proposing a unified scenario consistent with experimental data and predicting testable signals for future LHC runs.

Contribution

It demonstrates that the N2HDM can simultaneously accommodate the 95 GeV and 650 GeV Higgs anomalies within experimental constraints, offering a unified theoretical explanation.

Findings

A heavy Higgs at 650 GeV decays into a 125 GeV and a 95 GeV scalar.

Parameter regions in N2HDM Type-II and Type-Y fit the anomalies within 2σ.

Predictions include correlated signals in multiple final states for future LHC analyses.

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). 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 $2\sigma$ 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 $\gamma\gamma b\bar b$, $\tau^+\tau^- b\bar b$, $b\bar b\,\gamma\gamma$, and $\gamma\gamma\tau^+\tau^-$ final states.