Robustness of Inflation to Inhomogeneous Initial Conditions

TL;DR

This paper investigates how inhomogeneous initial conditions affect the robustness of small and large field inflation models, using numerical simulations to analyze their stability against gradient energies and initial inhomogeneities.

Contribution

It provides a comparative analysis of the robustness of small and large field inflation under inhomogeneous conditions through detailed numerical simulations.

Findings

Small field inflation is less robust to inhomogeneities than large field inflation.

Large field inflation withstands dominant gradient energies and initial inhomogeneities.

Inflation remains stable in open spacetimes even with initial collapsing regions.

Abstract

We consider the effects of inhomogeneous initial conditions in both the scalar field profile and the extrinsic curvature on different inflationary models. In particular, we compare the robustness of small field inflation to that of large field inflation, using numerical simulations with Einstein gravity in 3+1 dimensions. We find that small field inflation can fail in the presence of subdominant gradient energies, suggesting that it is much less robust to inhomogeneities than large field inflation, which withstands dominant gradient energies. However, we also show that small field inflation can be successful even if some regions of spacetime start out in the region of the potential that does not support inflation. In the large field case, we confirm previous results that inflation is robust if the inflaton occupies the inflationary part of the potential. Furthermore, we show that increasing initial scalar gradients will not form sufficiently massive inflation-ending black holes if the initial hypersurface is approximately flat. Finally, we consider the large field case with a varying extrinsic curvature K, such that some regions are initially collapsing. We find that this may again lead to local black holes, but overall the spacetime remains inflationary if the spacetime is open, which confirms previous theoretical studies.