Preheating from target space curvature and unitarity violation: Analysis in field space

TL;DR

This paper analyzes particle production and unitarity violation during preheating after inflation, deriving conditions based on target space curvature and inflaton potential, with implications for different inflation models.

Contribution

It introduces a semiclassical formula for particle spectra and a simple condition for unitarity violation during preheating, considering target space curvature and potential height.

Findings

Unitarity is violated in running kinetic and Higgs inflation.

Unitarity is conserved in α-attractor and Higgs-Palatini inflation.

Derived a condition linking target space curvature and inflaton potential to unitarity violation.

Abstract

We study particle production and unitarity violation caused by a curved target space right after inflation. We use the inflaton field value instead of cosmic time as the time variable, and derive a semiclassical formula for the spectrum of produced particles. We then derive a simple condition for unitarity violation during preheating, which we confirm by our semiclassical method and numerical solution. This condition depends not only on the target space curvature but also on the height of the inflaton potential at the end of inflation. This condition tells us, for instance, that unitarity is violated in running kinetic inflation and Higgs inflation, while unitarity is conserved in $\alpha$-attractor inflation and Higgs-Palatini inflation.