# Nonlinear preheating with nonminimally coupled scalar fields in the Starobinsky model

## TL;DR

This paper investigates the preheating process after inflation in the Starobinsky model with a nonminimally coupled scalar field, highlighting rescattering effects, inflaton particle production, and gravitational wave sources.

## Contribution

It provides the first lattice simulation analysis of rescattering and backreaction effects in nonminimally coupled scalar fields within the Starobinsky inflation model.

## Key findings

- Rescattering efficiently amplifies the scalar field variance.
- Inflaton particles can be produced via rescattering, affecting the condensate.
- Scalar metric perturbations have negligible impact on scalar field evolution.

## Abstract

We study the preheating after inflation in the Starobinsky model with a nonminimally coupled scalar field $\chi$. Using the lattice simulation, we analyze the rescattering between the $\chi$ particles and the inflaton condensate, and the backreaction effect of the scalar metric perturbations. We find that the rescattering is an efficient mechanism promoting the growth of the $\chi$ field variance. Meanwhile, copious inflaton particles can be knocked out of the inflaton condensate by rescattering. As a result, the inflaton field can become a nonnegligible gravitational wave source, even comparable with the $\chi$ field in some parameter regions. For the scalar metric perturbations, which are on the sub-Hubble scale in our analysis, our results show that they have negligible effects on the evolution of scalar fields and the production of gravitational waves in the model considered in present paper.