Explaining 95 GeV Anomalies in the 2-Higgs Doublet Model Type-I

TL;DR

The paper addresses whether a non-minimal Higgs sector in the 2HDM Type-I with an inverted mass hierarchy, placing the SM-like Higgs at $m_H=125$ GeV and a lighter neutral state near $95$ GeV, can reconcile LEP and LHC anomalies in $b\bar{b}$, $\gamma\gamma$, and $\tau^+\tau^-$ channels. It defines signal-strength observables $\mu_{\tau^+\tau^-}$, $\mu_{\gamma\gamma}$, and $\mu_{b\bar{b}}$ and performs MC scans of $(m_h,m_A,m_{H^\pm},\tan\beta,\sin(\beta-\alpha))$ under theoretical constraints (stability, unitarity, perturbativity) and experimental constraints (EW precision, HiggsBounds/Signals, $B$-physics). The results show a viable overlapping solution in which nearly degenerate $h$ and $A$ around $[94,96]$ GeV together explain the three excesses for $m_{H^\pm}$ in the range $152$–$168$ GeV and specific $\sin(\beta-\alpha)$ sign, while a purely CP-even explanation does not fit within $2\sigma$. The work provides a concrete benchmark point and emphasizes collider signatures unique to the inverted-hierarchy 2HDM Type-I for future tests.

Abstract

We show how the 2-Higgs Doublet Model (2HDM) Type-I can explain some excesses recently seen at the Large Hadron Collider (LHC) in $γγ$ and $τ^+τ^-$ final states in turn matching Large Electron Positron (LEP) data in $b\bar b$ signatures, all anomalies residing around 95 GeV. The explanation to such anomalous data is found in the aforementioned scenario when in inverted mass hierarchy, in two configurations: i) when the lightest CP-even Higgs state is alone capable of reproducing the excesses; ii) when a combination of such a state and the CP-odd Higgs boson is able to do so. To test further this scenario, we present some Benchmark Points (BPs) of it amenable to phenomenological investigation.

Figures (7)

• Figure 1: Results of the scan in Table \ref{['tab:scanrange']} mapped against the Higgs boson masses. The blue regions are allowed by stability, unitarity and perturbativity constraints while the red regions are allowed by Higgs data, $b \rightarrow s \gamma$ and EW precision constraints.
• Figure 2: Correlations amongst the signal strengths in Eq. (\ref{['Eq:sigstrength']}). Here, the total $\chi^2$ is displayed using the colour bar and the best fit point is given by the star marker. The ATLAS and CMS results with their corresponding $1 \sigma$ band are also represented.
• Figure 3: The value of $\sin(\beta-\alpha)$ plotted against $\chi^2_{\rm sum}$. The $\chi^2_{\rm min}$ is indicated by a star. The color gradient represents the strength of the coupling between the SM like Higgs boson and the pair of vector bosons.
• Figure 4: The di-photon signal strength results from experiment tensioned against the 2HDM Type-I predictions satisfying the three anomalies simultaneously.
• Figure 5: Results of the scan in Table \ref{['tab:scanrangeeven']} mapped against the Higgs masses. The blue regions are allowed by stability, unitarity and perturbativity constraints while the red regions are allowed by Higgs data, $b \rightarrow s \gamma$ and EW precision constraints.