# Preheating in Full General Relativity

## TL;DR

This paper explores the role of full general relativity in the non-linear dynamics of preheating after inflation, using numerical methods to assess gravitational effects and their impact on early universe processes.

## Contribution

It introduces three numerical methods for studying preheating in full general relativity, extending beyond perturbation theory and classical assumptions.

## Key findings

- Perturbation theory fails for horizon-scale modes.
- Preheating remains viable without black hole formation.
- Full relativity does not necessarily disrupt preheating dynamics.

## Abstract

We investigate the importance of local gravity during preheating, the non-linear dynamics that may be responsible for starting the process of reheating the universe after inflation. We introduce three numerical methods that study a simple preheating scenario while relaxing gravitational assumptions, culminating in studying the process in full numerical relativity. We confirm that perturbation theory is no longer valid when one considers modes whose wavelengths are comparable to the size of the horizon at the end of inflation; however, this breakdown does not necessarily lead to a breakdown of the preheating process in non-linear gravity. For the specific model we test we find no evidence for the creation of primordial black holes from the instabilities in this model. Finally, we remark on the opportunity for future numerical study of non-linear gravitational dynamics in the early universe.