On the Unruh effect in de Sitter space

TL;DR

This paper interprets the de Sitter universe's temperature as a dynamical Unruh effect linked to the Hubble sphere, showing that certain observers can detect this effect as approximately thermal radiation.

Contribution

It provides a novel interpretation of de Sitter temperature through a dynamical Unruh effect and analyzes the detectability and stability of Kodama observers in this context.

Findings

Kodama observers detect approximately thermal Unruh radiation.

Back-reaction estimates suggest stable trajectories for Kodama observers.

The effect is analogous to quantum noise perceived by accelerated observers.

Abstract

We give an interpretation of the temperature in de Sitter universe in terms of a dynamical Unruh effect associated with the Hubble sphere. As with the quantum noise perceived by a uniformly accelerated observer in static space-times, observers endowed with a proper motion can in principle detect the effect. In particular, we study a "Kodama observer" as a two-field Unruh detector for which we show the effect is approximately thermal. We also estimate the back-reaction of the emitted radiation and find trajectories associated with the Kodama vector fields are stable.