Mass bounds of the lightest CP-even Higgs boson in the two-Higgs-doublet model

TL;DR

This paper investigates the theoretical bounds on the lightest Higgs boson mass in the two-Higgs-doublet model, considering the effects of a cutoff scale and experimental constraints, revealing significant differences from the Standard Model.

Contribution

It provides new bounds on the lightest Higgs mass in 2HDM based on renormalization group analysis and compares them with the Standard Model, including the impact of experimental constraints.

Findings

Lower bound on Higgs mass can be as low as 100 GeV for high cutoff scales.

Upper bound remains similar to the Standard Model.

Small Higgs masses are excluded in Model II due to $b o s \, \gamma$ constraints.

Abstract

The upper and the lower bounds of the lightest CP-even Higgs-boson mass ($m_h$) are discussed in the two-Higgs-doublet model (2HDM) with a softly-broken discrete symmetry. They are obtained as a function of a cut-off scale $\Lambda$ ($\leq 10^{19}$ GeV) by imposing the conditions in which the running coupling constants neither blow up nor fall down below $\Lambda$. In comparison with the standard model (SM), although the upper bound does not change very much, the lower bound is considerably reduced. In the decoupling regime where only one Higgs boson ($h$) becomes much lighter than the others, the lower bound is given, for example, by about 100 GeV for $\Lambda = 10^{19}$ GeV and $m_t = 175$ GeV, which is smaller by about 40 GeV than the corresponding lower bound in the SM. In generic cases, $m_h$ is no longer bounded from below by these conditions. If we consider the $b \to s \gamma$ constraint, small values of $m_h$ are excluded in Model II of the 2HDM.