Cosmological Correlators for Bogoliubov Initial States

TL;DR

This paper develops a framework to compute late-time correlators in de Sitter space for Bogoliubov initial states by relating them to Euclidean AdS Witten diagrams, revealing new insights into their structure and singularities.

Contribution

It introduces a reformulation of late-time dS correlators for Bogoliubov states using EAdS Witten diagrams, extending Mellin space techniques to generic dS invariant vacua.

Findings

Correlators can be expressed via EAdS Witten diagrams involving antipodal points.

Identifies the role of antipodal maps in generating solutions with collinear singularities.

Provides a position space interpretation of conformal Ward identities for these correlators.

Abstract

We consider late-time correlators in de Sitter (dS) space for initial states related to the Bunch-Davies vacuum by a Bogoliubov transformation. We propose to study such late-time correlators by reformulating them in the familiar language of Witten diagrams in Euclidean anti-de Sitter space (EAdS), showing that they can be perturbatively re-cast in terms of corresponding dS boundary correlators in the Bunch-Davies vacuum and in turn, Witten diagrams in EAdS. Unlike the standard relationship between late-time correlators in the Bunch-Davies vacuum and EAdS Witten diagrams, this involves points on the upper and lower sheet of the EAdS hyperboloid which account for antipodal singularities of the two-point functions. Such Bogoliubov states include an infinite one parameter family of de Sitter invariant vacua as a special case, where the late-time correlators are constrained by Conformal Ward identities. In momentum space, it is well known that their late-time correlators exhibit singularities in collinear ("folded") momentum configurations. We give a position space interpretation of such solutions to the conformal Ward identities, where in embedding space they can be generated from the solution without collinear singularities by application of the antipodal map. We also discuss the operator product expansion (OPE) limit of late-time correlators in a generic dS invariant vacuum. Many results are derived using the Mellin space representation of late-time correlators, which in this work we extend to accommodate generic dS invariant vacua.