New limits on $\mathbf{\tan\beta}$ for 2HDMs with $\mathbf{Z_2}$ symmetry

TL;DR

This paper derives new bounds on the parameters of two-Higgs-doublet models with Z2 symmetry, based on theoretical and experimental constraints, refining the allowed range of tanβ and scalar masses.

Contribution

It provides updated limits on heavy scalar masses and tanβ in 2HDMs with Z2 symmetry, incorporating unitarity, stability, and flavor constraints, including effects of soft symmetry breaking.

Findings

Heavy scalar masses are constrained below 1 TeV.

Tanβ is limited between 1/8 and 8 under certain conditions.

Soft breaking allows larger tanβ values with correlated scalar masses.

Abstract

In two-Higgs-doublet models with exact $Z_2$ symmetry, putting $m_h \simeq 125$ GeV at the alignment limit, the following limits on the heavy scalar masses are obtained from the conditions of unitarity and stability of the scalar potential: $m_H,~m_A,~m_{H^+} < 1$ TeV and $1/8 <\tan\beta <8$. The constraints from $b \to s \gamma$ and neutral meson mass differences, when superimposed on the unitarity constraints, put a tighter lower limit on $\tan\beta$ depending on $m_{H^+}$. It has also been shown that larger values of $\tan\beta$ can be allowed by introducing soft breaking term in the potential at the expense of a correlation between $m_H$ and the soft breaking parameter.