Alignment, reverse alignment, and wrong sign Yukawa couplings in two Higgs doublet models

TL;DR

This paper explores various limits of two Higgs doublet models with a softly broken U(1) symmetry, analyzing naturalness, stability, and experimental constraints, and calculating decay rates in specific parameter regimes.

Contribution

It systematically studies alignment, reverse alignment, and wrong sign Yukawa couplings in 2HDMs, incorporating naturalness and phenomenological constraints.

Findings

Allowed scalar masses depend on naturalness and stability criteria.

The $h\to \gamma\gamma$ decay rate is computed in the wrong sign Yukawa limit.

Parameter space is constrained by unitarity, the $\rho$ parameter, and perturbativity.

Abstract

We consider two Higgs doublet models with a softly broken U(1) symmetry, for various limiting values of the scalar mixing angles $\alpha$ and $\beta$. These correspond to the Standard Model Higgs particle being the lighter CP-even scalar (alignment) or the heavier CP-even scalar (reverse alignment), and also the limit in which some of the Yukawa couplings of this particle are of the opposite sign from the vector boson couplings (wrong sign). In these limits we impose a criterion for naturalness by demanding that quadratic divergences cancel at one loop. We plot the allowed masses of the remaining physical scalars based on naturalness, stability, perturbative unitarity and constraints coming from the $\rho$ parameter. We also calculate the $h\to \gamma\gamma$ decay rate in the wrong sign limit.