On unitarity in singlet inflation with a non-minimal coupling to gravity

TL;DR

This paper investigates unitarity constraints in singlet inflation models with non-minimal gravity coupling, highlighting the importance of collective effects during preheating and establishing an upper bound on the coupling strength.

Contribution

It provides a detailed analysis of unitarity issues in singlet inflation with non-minimal coupling, emphasizing the role of collective scattering effects during preheating.

Findings

Particle production is less efficient than in Higgs inflation.

Unitarity violation at large couplings requires special treatment.

Upper bound on non-minimal coupling is of order a few hundreds.

Abstract

We study inflationary models based on a non-minimal coupling of a singlet scalar to gravity, focussing on the preheating dynamics and the unitarity issues in this regime. If the scalar does not have significant couplings to other fields, particle production after inflation is far less efficient than that in Higgs inflation. As a result, unitarity violation at large non-minimal couplings requires a different treatment. We find that collective effects in inflaton scattering processes during preheating make an important impact on the unitarity constraint. Within effective field theory, the consequent upper bound on the non-minimal coupling is of order a few hundreds.