Restricting the parameter space of type-II two-Higgs-doublet models with CP violation

Abstract

We explore the parameter space of the type-II two-Higgs-doublet model with softly broken ${Z}_{2}$ symmetry, allowing for $CP$ violation in the scalar potential. Imposing theory-motivated and experimentally-driven constraints, we show that as the $CP$-violating phases are increased, only small regions of parameter space survive, including regions slightly away from the alignment limit. Electroweak oblique parameters and electric dipole moments emerge as most restrictive constraints. We show that imposing these constraints (as well as theoretical bounds such as perturbativity) the masses of the charged and heavy neutral Higgs, unlike in the $CP$ conserving case, are bound from above and below. In particular, the heavy neutral Higgs masses are almost degenerate. In this parameter space region we highlight the relevant decay signals of the heavy neutral Higgs, involving both $Zh$ and $WW/ZZ$, indicative of $CP$ violation in the model.