Unitarity constraints on scalar parameters of the Standard and Two Higgs Doublets Model

Abstract

Unitarity constraints on the scalar parameters both for the Standard Model and the general Two Higgs Doublet Model (THDM) are examined. In the case of the THDM with an exact discrete symmetry transformation, we show that the mass of the lightest CP-even Higgs boson ($M_h$) and $\tan\beta$ are strongly correlated and consequently a strong lower bound can be put on $M_h$ for large $\tan\beta$. It is also shown that the inclusion of the discrete symmetry breaking term relaxes the aforementioned correlation.