Islands in Kerr-de Sitter spacetime and their flat limit

TL;DR

This paper investigates the information paradox in Kerr-de Sitter spacetimes using quantum extremal islands, demonstrating the emergence of Page curves and analyzing the flat space limit to connect with flat cosmology results.

Contribution

It introduces a method to locate quantum extremal islands outside the cosmological horizon in Kerr-de Sitter spacetime and explores their flat limit, extending previous flat-space results.

Findings

Island regions cause entropy to follow the Page curve.

Quantum extremal surfaces are located outside the cosmological horizon.

Pure de Sitter spacetime acts as a fast scrambler.

Abstract

We use quantum extremal island method to study the information paradox on certain cosmological setups known as three dimensional Kerr-de Sitter spacetimes. To do so, we couple an auxiliary flat bath system to this spacetime in timelike singularity and measure entropy of hawking radiation in its asymptotic regions where the gravity is weak. We show that adding island regions to the entanglement wedge of radiation causes its entropy to obey Page curve. The boundary of island i.e. quantum extremal surface is located outside the cosmological horizon in the region connected directly to the bath. Taking the flat-space limit from the location of island and its related calculation in the Kerr-de Sitter sapcetime results in the flat-space cosmology (FSC) island, scrambling time and also Page time that were obtained in our previous paper. We repeat the same calculation for the pure de Sitter spacetime and show that our setup which neglects the effect of backreaction, leads also to a quantum extremal surface outside the cosmological horizon. We calculate the scrambling time and confirm the idea that pure de Sitter spacetime is a fast scrambler.