Robustness of inflation to kinetic inhomogeneities

TL;DR

This paper examines how large inhomogeneities in the inflaton field and its momentum impact the duration and robustness of inflation, revealing that sub-Planckian models are less robust to kinetic perturbations than super-Planckian ones.

Contribution

It provides a detailed analysis of the effects of kinetic inhomogeneities on inflation's robustness, extending previous findings and highlighting the dependence on characteristic scales and initial conditions.

Findings

Large kinetic perturbations generally reduce the number of e-folds.

Sub-Planckian models are less robust to inhomogeneities unless initial conditions are far from the minimum.

Super-Planckian models maintain robustness despite initial sub-dominance of potential energy.

Abstract

We investigate the effects of large inhomogeneities in both the inflaton field and its momentum. We find that in general, large kinetic perturbations reduce the number of e-folds of inflation. In particular, we observe that inflationary models with sub-Planckian characteristic scales are not robust even to kinetic energy densities that are sub-dominant to the potential energy density, unless the initial field configuration is sufficiently far from the minimum. This strengthens the results of our previous work. In inflationary models with super-Planckian characteristic scales, despite a reduction in the number of e-folds, inflation is robust even when the potential energy density is initially sub-dominant. For the cases we study, the robustness of inflation strongly depends on whether the inflaton field is driven into the reheating phase by the inhomogeneous scalar dynamics.