Ultraviolet behaviour of Higgs inflation models

TL;DR

This paper investigates the high-energy behavior of Higgs inflation models, demonstrating that their scattering amplitudes remain well-behaved up to the Planck scale, regardless of formulation or added terms.

Contribution

It shows that Higgs inflation models are UV safe at tree level above the unitarity violation scale, across different formulations and with additional curvature terms.

Findings

Tree-level amplitudes are well-behaved below the Planck scale.

Results are consistent in metric and Palatini formulations.

Adding an R^2 term does not affect the high-energy behavior.

Abstract

We study the ultraviolet behaviour of Higgs inflation models above the apparent unitarity violation scale arising from the large non minimal coupling to gravity, by computing on-shell 4-point scattering amplitudes in the presence of a large inflaton background, away from the electroweak vacuum. We find that all tree-level amplitudes are well behaved at high energies below the inflaton background that can thus take values up to the Planck scale. This result holds in both the metric and Palatini formulation, and is independent of the frame (Jordan or Einstein) as expected. The same result also holds if an $R^2$ term is added to the action.