Unitarity-violation in Generalized Higgs Inflation Models

TL;DR

This paper analyzes the energy scale at which unitarity-violation occurs in generalized Higgs inflation models with multiple scalars, showing hierarchies in non-minimal couplings can push this scale above the Planck level.

Contribution

It provides a detailed examination of unitarity-violation scales in models with multiple scalars, highlighting how coupling hierarchies affect these scales.

Findings

Equal non-minimal couplings match existing unitarity-violation results.

Hierarchies in couplings can raise the violation scale above the Planck scale.

Models attempting to resolve unitarity issues are discussed.

Abstract

Unitarity-violation presents a challenge for non-minimally coupled models of inflation based on weak-scale particle physics. We examine the energy scale of tree-level unitarity-violation in scattering processes for generalized models with multiple scalar fields where the inflaton is either a singlet scalar or the Higgs. In the limit that the non-minimal couplings are all equal (e.g. in the case of Higgs or other complex inflaton), the scale of tree-level unitarity-violation matches the existing result. However if the inflaton is a singlet, and if it has a larger non-minimal coupling than other scalars in the model, then this hierarchy increases the scale of tree-level unitarity-violation. A sufficiently strong hierarchy pushes the scale of tree-level unitarity-violation above the Planck scale. We also discuss models which attempt to resolve the issue of unitarity-violation in Higgs Inflation.