Restoring the sting to metric preheating

TL;DR

This paper investigates the fragility of suppression of super-Hubble metric perturbations during preheating, showing it depends on specific interaction forms and is absent in more realistic models, leading to observable effects.

Contribution

It demonstrates that suppression of super-Hubble perturbations during preheating is fragile and depends on the interaction details, contrasting simple models with realistic particle physics scenarios.

Findings

Suppression of super-Hubble metric perturbations is sensitive to interaction specifics.

Realistic models often lack suppression, allowing perturbation growth.

Multiple observable phenomena, including magnetic fields and non-Gaussianities, can arise.

Abstract

The relative growth of field and metric perturbations during preheating is sensitive to initial conditions set in the preceding inflationary phase. Recent work suggests this may protect super-Hubble metric perturbations from resonant amplification during preheating. We show that this possibility is fragile and sensitive to the specific form of the interactions between the inflaton and other fields. The suppression is naturally absent in two classes of preheating in which either (1) the vacua of the non-inflaton fields during inflation are deformed away from the origin, or (2) the effective masses of non-inflaton fields during inflation are small but during preheating are large. Unlike the simple toy model of a $g^2 \phi^2 \chi^2$ coupling, most realistic particle physics models contain these other features. Moreover, they generically lead to both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble scales. Large-scale coherent magnetic fields may also appear naturally.