Could the 650 GeV excess be a pseudoscalar of a 3-Higgs doublet model?

Abstract

In this study, we propose the interpretation of a 650 GeV excess observed at the Large Hadron Collider (LHC) by the CMS Collaboration in terms of the production of a CP-odd (or pseudoscalar)Higgs boson A, with mass around 650 GeV, decaying into the Standard Model (SM)-like Higgs state h125 (in turn decaying into γγ) and a Z boson (in turn decaying into b¯b), within a 3-HiggsDoublet Model (3HDM) featuring two active and one inert doublet, known as the I(1+2)HDM. This theoretical structure features a spectrum with both the SM-like Higgs boson (with a 125GeV mass) and a lighter CP-even (or scalar) Higgs state with mass around 95 GeV, h95, which is present in this scenario for the purpose of simultaneously explaining anomalies seen in the b¯b, γγand τ+τ− final states in searches for additional light Higgs states at the Large Electron-Positron(LEP) collider and LHC itself. It should be noted that, in the I(1+2)HDM, the inert sector presents loop-induced enhancements to the h95 → γγ width via additional scalar charged states, providing a viable mechanism to explain, in particular, the observed (and most significant) di-photon excess at95 GeV. Taking into account both experimental and theoretical constraints, our results can not only explain the aforementioned anomalies (possibly, aside from the τ+τ−, which is the most marginal one) but also predict, as collateral signals, resonant production of the same CP-odd scalar A followed by the decays: (i) A → h95 Z, leading to the same γγb¯b final state displaying the original 650 GeV anomaly and (ii) A → tt¯, leading to a well-known and studied signature. Both of these signals are potentially explorable at Run 3 of the LHC and most possibly so at the High-Luminosity LHC(HL-LHC), while being consistent with current data at a significance level of 2.5σ.

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Identifiers

ORCID for Stefano Moretti: orcid.org/0000-0002-8601-7246

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