Unitarity constraints on general scalar couplings with SARAH

TL;DR

This paper updates the SARAH package to compute unitarity constraints on scalar couplings in BSM models, including all relevant energy contributions, enabling more accurate bounds on scalar interactions.

Contribution

The new version of SARAH can analytically and numerically evaluate two-particle scalar scattering matrices without high-energy approximations, improving unitarity constraint calculations.

Findings

Constraints on trilinear scalar couplings can be derived.

Including all energy contributions can alter bounds on quartic couplings.

Application to a singlet extended Standard Model demonstrates the method.

Abstract

We present an update of the Mathematica package SARAH to calculate unitarity constraints in BSM models. The new functions can perform an analytical and numerical calculation of the two-particle scattering matrix of (uncoloured) scalars. We do not make use of the simplifying assumption of a very large scattering energy, but include all contributions which could become important at small energies above the weak scale. This allows us to constrain trilinear scalar couplings. However, it can also modify (weakening or strengthening) the constraints on quartic couplings, which we show via the example of a singlet extended Standard Model.