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.
Highlights
Inflation is a successful paradigm that describes the beginning of the universe and provides seeds for large scale structure and the cosmic microwave background (CMB) anisotropies
We study particle production and unitarity violation caused by a curved target space right after inflation
We have studied particle production and unitarity violation in inflationary models with multiple scalar fields and a curved target space during preheating after inflation
Summary
Inflation is a successful paradigm that describes the beginning of the universe and provides seeds for large scale structure and the cosmic microwave background (CMB) anisotropies. The unitarity violation of Higgs inflation was originally found by studying the dynamics of the inflaton in the Jordan frame, but this is nicely understood as a result of the target space curvature in the Einstein frame [6,7]. We find that the following simple condition works as a criterion for unitarity violation: VðΦÞ ≳ Λ4; ð1:1Þ where VðΦÞ is the height of the inflaton potential at the end of inflation with Φ the inflaton amplitude, and Λ is the typical mass scale of the target space curvature. Our main focus is on the preheating dynamics after inflation, particle production and unitarity violation from the target space curvature are possible even beyond. IV, with comments on possible UV completions of running kinetic inflation and Higgs inflation
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