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

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 α-attractor inflation and Higgs-Palatini inflation.

Tachyonic Preheating in Plateau Inflation

“…The same unitarity bound, U 0 Λ 4 cut , was derived in Ref. [59], although not in the context of tachyonic preheating.…”

Low-energy probes of small CMB amplitude in models of radiative Higgs mechanism

“…As for the preheating, it was found that the effective mass of φ becomes tachyonic after inflation [55], so that careful analyses are often necessary to estimate particle productions and resulting reheat temperature; see for example [56][57][58] and references therein.…”