Does Palatini Higgs Inflation Conserve Unitarity?

TL;DR

This paper argues that Palatini Higgs Inflation preserves unitarity up to the Planck scale, unlike the metric formulation, potentially making it a more consistent model of early universe inflation.

Contribution

It reexamines unitarity in Palatini Higgs Inflation and suggests it remains valid at all relevant energies, contrasting with previous beliefs about metric formulation.

Findings

No unitarity violation in Palatini Higgs scattering below Planck scale

Palatini Higgs Inflation is consistent up to quantum gravity energies

Potential advantage of Palatini over metric Higgs Inflation

Abstract

In the conventional metric formulation of gravity, the Higgs Inflation model violates unitarity in the electroweak vacuum in Higgs scattering at the energy scale $\Lambda \sim M_{Pl}/\xi$, where $\xi \sim 10^4$ is the non-minimal coupling of the Higgs to the Ricci scalar. In the Palatini formulation it is commonly believed that $\Lambda \sim M_{Pl}/\sqrt{\xi}$, where $\xi \sim 10^{9}$. Here we reconsider unitarity violation in the electroweak vacuum in the Palatini formulation. We argue that there is no unitarity violation in Higgs scattering in the Palatini non-minimally coupled Standard Model in the electroweak vacuum at energies below the Planck scale. In this case Palatini Higgs Inflation completely conserves unitarity and is consistent at all energies up to those at which quantum gravity becomes important. If true, this would imply that Palatini Higgs Inflation has a significant advantage over metric Higgs Inflation.