Constraints on light scalars in the Aligned-two-Higgs-doublet model

Abstract

In this work, we explore the viability of light-scalar scenarios within the $\mathcal{C}\mathcal{P}$-conserving, flavour-aligned two-Higgs-doublet model (A2HDM), where at least one additional neutral or charged scalar is assumed to be lighter than the 125 GeV Higgs boson. The A2HDM naturally avoids flavour-changing neutral currents via Yukawa alignment, providing a more flexible framework than conventional $Z_2$-symmetric models. Employing the $\text{HEPfit}$ package within a Bayesian statistical approach, we perform global fits across all distinct light-scalar configurations, incorporating theoretical requirements and experimental constraints from electroweak precision observables, flavour data, Higgs measurements, and direct searches at the LEP and the LHC.

Comments: Contribution to the 2025 Electroweak session of the 59th Rencontres de Moriond