Nonperturbative infrared enhancement of nonGaussian correlators in de Sitter space

TL;DR

This paper analyzes the four-point correlation function of a light scalar field in de Sitter space, revealing significant infrared enhancement of loop contributions and the emergence of new exchange-like momentum structures.

Contribution

It provides a nonperturbative calculation of four-point correlators in de Sitter space, showing infrared effects can dominate and modify the expected contact interaction structure.

Findings

Loop contributions are comparable to tree-level in the infrared limit.

Infrared effects induce a new exchange-like momentum structure.

Tree-level momentum structure is renormalized by a factor of order unity.

Abstract

We compute the four-point correlation function of a light O(N) scalar field in de Sitter space in the large-N limit. For superhorizon momentum modes, infrared effects strongly enhance the size of loop contributions. We find that in the deep infrared limit, the latter are of the same order as the tree-level one. The tree-level momentum structure, characteristic of a contact term, gets renormalized by a factor of order unity. In addition loop contributions give rise to a new momentum structure, characteristic of an exchange diagram, corresponding to the exchange of an effective composite scalar degree of freedom.