Unitarity constraints on 2HDM with higher dimensional operators

TL;DR

This paper explores how perturbative unitarity constraints limit the parameter space of the 2HDM when including dimension-six operators, affecting scalar production and electroweak precision bounds.

Contribution

It provides the first comprehensive analysis of unitarity bounds on higher-dimensional operators in the 2HDM framework, linking high-energy consistency with experimental constraints.

Findings

Higher-dimensional operators can significantly enhance scalar production in vector boson fusion.

Unitarity bounds restrict certain Wilson coefficients, especially those poorly constrained by electroweak data.

Some parameter space regions are excluded when combining unitarity with electroweak precision constraints.

Abstract

We study how the requirement of perturbative unitarity restricts the parameter space of the two-Higgs-doublet model (2HDM) when higher-dimensional operators up to dimension six are included. We demonstrate that such operators can enhance scalar production cross sections in vector boson fusion relative to 2HDM. Using S-matrix unitarity, we place bounds on several dimension-six bosonic operators. We also find that certain blind directions in the Wilson coefficients of T-parameter violating operators which are poorly constrained by electroweak precision data can be partially excluded when unitarity constraints are taken into account. These results demonstrate how high-energy consistency can complement experimental limits in defining the allowed parameter space of 2HDM effective field theory.