Massless Metric Preheating

TL;DR

This paper demonstrates that super-Hubble metric perturbations can grow exponentially during preheating, significantly affecting particle production and relic abundance calculations, with an analytical proof and consideration of backreaction effects.

Contribution

It provides an analytical proof of exponential growth of super-Hubble metric perturbations during preheating and explores their impact on field variances and particle production.

Findings

Super-Hubble metric perturbations can grow exponentially during preheating.

Ignoring metric perturbations underestimates maximum field variances.

Metric perturbations enhance resonance channels, affecting relic abundance estimates.

Abstract

Can super-Hubble metric perturbations be amplified exponentially during preheating ? Yes. An analytical existence proof is provided by exploiting the conformal properties of massless inflationary models. The traditional conserved quantity \zeta is non-conserved in many regions of parameter space. We include backreaction through the homogeneous parts of the inflaton and preheating fields and discuss the role of initial conditions on the post-preheating power-spectrum. Maximum field variances are strongly underestimated if metric perturbations are ignored. We illustrate this in the case of strong self-interaction of the decay products. Without metric perturbations, preheating in this case is very inefficient. However, metric perturbations increase the maximum field variances and give alternative channels for the resonance to proceed. This implies that metric perturbations can have a large impact on calculations of relic abundances of particles produced during preheating.