A Tail of Eternal Inflation

TL;DR

This paper explores how non-Gaussian features of primordial fluctuations influence the transition to eternal inflation, revealing that certain aspects depend on physics beyond the effective field theory and require UV completion.

Contribution

It demonstrates that the phase transition to eternal inflation is sensitive to the non-Gaussian tail of fluctuations, which are incalculable within standard EFT and depend on UV physics.

Findings

Eternal inflation transition depends on non-Gaussian tail physics.

Large fluctuations for eternal inflation require UV completion.

Breakdown of perturbative description relates to de Sitter entropy.

Abstract

Non-trivial inflaton self-interactions can yield calculable signatures of primordial non-Gaussianity that are measurable in cosmic surveys. Surprisingly, we find that the phase transition to slow-roll eternal inflation is often incalculable in the same models. Instead, this transition is sensitive to the non-Gaussian tail of the distribution of scalar fluctuations, which probes physics inside the horizon, potentially beyond the cutoff scale of the Effective Field Theory of Inflation. We demonstrate this fact directly by calculating non-Gaussian corrections to Stochastic Inflation within the framework of Soft de Sitter Effective Theory, from which we derive the associated probability distribution for the scalar fluctuations. We find parameter space consistent with current observations and weak coupling at horizon crossing in which the large fluctuations relevant for eternal inflation can only be determined by appealing to a UV completion. We also show this breakdown of the perturbative description is required for the de Sitter entropy to reflect the number of de Sitter microstates.