Instability of de Sitter space under thermal radiation in different vacua

TL;DR

This paper investigates how de Sitter space's stability is affected by thermal radiation in various vacua, revealing that the horizon area can increase or decrease depending on the mode contributions, indicating potential instability.

Contribution

It provides an explicit analysis of scalar field modes and energy-momentum tensor behavior in different vacua, highlighting the impact on de Sitter horizon stability.

Findings

Horizon area increases with incoming modes

Horizon area decreases with outgoing modes

Mode functions can be separated into incoming and outgoing components

Abstract

We study the instability of de Sitter space-time (dS) under thermal radiation in different vacua. We argue that the mode function solution of a scalar field in four-dimensional dS can be separated into the incoming and outgoing modes. Different vacua for dS are realized by different combinations of positive frequency modes assigned to each solution. For a minimally coupled massless scalar field, we explicitly compute the behavior of the mode function and the corresponding energy-momentum tensor in the Unruh vacuum near the horizon, and find that the horizon area increases (decreases) in time when the incoming (outgoing) mode contributes to thermal flux.