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

TL;DR

This paper investigates how unitarity constraints limit scalar parameters in the Standard Model and Two Higgs Doublet Model, revealing correlations between Higgs mass and model parameters, and how symmetry breaking affects these bounds.

Contribution

It provides a detailed analysis of unitarity constraints on scalar parameters in both models, highlighting the impact of discrete symmetry and its breaking.

Findings

Strong correlation between Higgs mass and tanβ in THDM with exact symmetry

Lower bounds on Higgs mass for large tanβ

Relaxation of bounds when symmetry breaking terms are included

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.