Influence Phase of a dS Observer I : Scalar Exchange

TL;DR

This paper introduces a method to compute the influence phase of a de Sitter observer interacting with scalar fields, capturing radiation reaction and Hawking radiation effects, with applications to open quantum systems in cosmology.

Contribution

It presents a novel approach inspired by AdS black hole computations to determine the influence phase in de Sitter space, including finite size effects and covariant cubic corrections.

Findings

Derived the influence phase using on-shell action on doubled spacetime.

Reproduced flat-space radiation reaction in the short-time limit.

Identified recursive structures across spacetime dimensions.

Abstract

Inspired by real-time computations in AdS black holes, we propose a method to obtain the influence phase of a cosmological observer by calculating the on-shell action on a doubled spacetime geometry. The influence phase is the effective action for an open system: for a dS static patch observer coupled to a scalar field it incorporates the radiation reaction due to the bulk fields and their dS Hawking radiation. For a general extended source in dS, we describe how to account for finite size effects. In the long-time limit, we get a Markovian open quantum system susceptible to cosmological fluctuations, whereas the short-time limit reproduces the worldline theory of flat-space radiation reaction. We also present a fully covariantised form for the cubic corrections to the radiation reaction in even spacetime dimensions, including Hubble contributions, and find an intriguing recursive structure across dimensions.