Can a pseudoscalar with a mass of 365 GeV in two-Higgs-doublet models explain the CMS tt¯ excess?

Abstract

We investigate the recently reported tt¯ excess by the CMS Collaboration within the framework of conventional Two-Higgs-Doublet Models (2HDMs). Considering all four types (I, II, X, and Y), we perform a comprehensive parameter space scan using the best-fit values for a pseudoscalar boson A: MA=365 GeV, ΓA/MA=2%, and tan⁡β=1.28. Theoretical requirements and experimental constraints are systematically applied, including conditions from a bounded-below scalar potential, vacuum stability, unitarity, perturbativity, Flavor-Changing Neutral Currents (FCNCs), and direct searches at high-energy colliders. Our analysis shows that perturbativity imposes upper bounds of around 723 GeV on MH± and MH. FCNC constraints exclude all viable parameter space in Types II and Y, while a small region persists in Types I and X, but this region is ultimately ruled out by recent tt¯Z measurements by the ATLAS and CMS Collaborations at the LHC. We conclude that conventional 2HDMs alone cannot accommodate a pseudoscalar boson that explains the observed tt¯ excess within viable parameter space. However, incorporating toponium effects in the background fit could potentially alter this conclusion.

Keywords

• Higgs physics
• Beyond the Standard Model
• Electroweak precision data