Higgs-Palatini Inflation and Unitarity

TL;DR

This paper demonstrates that Higgs inflation in the Palatini formulation avoids unitarity violation, making it UV-safe and more predictive compared to the metric formulation, which suffers from unitarity issues.

Contribution

It shows that Higgs inflation in the Palatini formulation does not have unitarity problems, unlike the metric formulation, thus providing a UV-safe inflationary model.

Findings

UV cutoff is much higher than the Hubble rate in Palatini formulation

Higgs-Palatini inflation is UV-safe and minimal

Inflationary dynamics are unaffected by unknown UV physics

Abstract

In the Higgs inflation scenario the Higgs field is strongly coupled to the Ricci scalar in order to drive primordial inflation. However, in its original form in pure metric formulation of gravity, the ultraviolet (UV) cutoff of the Higgs interactions and the Hubble rate are of the same magnitude, and this makes the whole inflationary evolution dependent of the unknown UV completion of the Higgs sector. This problem, the unitarity violation, plagues the Higgs inflation scenario. In this letter we show that, in the Palatini formulation of gravitation, Higgs inflation does not suffer from unitarity violation since the UV cutoff lies parametrically much higher than the Hubble rate so that unknown UV physics does not disrupt the inflationary dynamics. Higgs-Palatini inflation, as we call it, is, therefore, UV-safe, minimal and endowed with predictive power.