On Preheating in Higgs Inflation

TL;DR

This paper examines the unitarity issues during preheating in Higgs inflation, showing that these problems depend on higher-dimensional operators and can be mitigated by their effects on background dynamics and fluctuations.

Contribution

It demonstrates how higher-dimensional operators influence unitarity and particle production during preheating in Higgs inflation, providing numerical analysis with specific operators.

Findings

Unitarity violation is linked to strong coupling issues influenced by higher-dimensional operators.

Particle energies during preheating can stay below the theory's cutoff scale.

Numerical calculations confirm the impact of four-derivative operators on particle production.

Abstract

Recently, the problem of unitarity violation during the preheating stage of Higgs inflation with a large non-minimal coupling has been much discussed in the literature. We point out that this problem can be translated into a strong coupling problem for the dimensionless effective coupling, and that the existence of these problems is highly dependent on the choice of higher-dimensional operators because they can significantly change the background dynamics and the canonical normalization of the fluctuations around it. Correspondingly, the typical energy of particles produced during the first stage of preheating can remain comparable to or below the cutoff scale of the theory. As an example, we numerically calculate the particle production in the presence of a specific four-derivative operator of the Higgs field, and confirm the statement above. Our argument also applies to multi-field inflation with non-minimal couplings.