The hand-made tail: Non-perturbative tails from multifield inflation

TL;DR

This paper investigates how non-perturbative effects in multifield inflation influence the probability distribution tails of primordial fluctuations, which are crucial for understanding rare events like primordial black holes.

Contribution

It introduces a stochastic inflation approach to analyze non-Gaussian tails in multifield models, revealing their generic enhancement during slow-roll inflation.

Findings

Non-Gaussian tails are a common feature in multifield inflation.

Standard perturbation theory fails to capture tail behavior.

Enhanced tails could impact primordial black hole formation.

Abstract

It is becoming increasingly clear that large but rare fluctuations of the primordial curvature field, controlled by the tail of its probability distribution, could have dramatic effects on the current structure of the universe -- {\it e.g.} via primordial black-holes. However, the use of standard perturbation theory to study the evolution of fluctuations during inflation fails in providing a reliable description of how non-linear interactions induce non-Gaussian tails. Here, we use the stochastic inflation formalism to study the non-perturbative effects from multi-field fluctuations on the statistical properties of the primordial curvature field. Starting from the effective action describing multi-field fluctuations, we compute the joint probability density function and show that enhanced non-Gaussian tails are a generic feature of slow-roll inflation with additional degrees of freedom.