Islands for black holes in a hybrid quantum state

TL;DR

This paper investigates a regular spacetime solution in a hybrid quantum state within the RST model, confirming the Page curve for radiation entropy and examining the role of islands in black hole entropy.

Contribution

It demonstrates that the radiation entropy follows a Page curve in a regular spacetime and shows that islands do not contribute to the generalized black hole entropy in this context.

Findings

Radiation entropy follows a Page curve.

Islands do not contribute to black hole entropy.

Spacetime remains completely regular with a causal diamond structure.

Abstract

Following our previous work on hybrid quantum states in the RST model, we study its most interesting solution representing a completely regular spacetime with the structure of causal diamond, containing an apparent horizon and radiation at infinity. Adapting recent computations of radiation entropy in terms of the entropy of entanglement, we find that this entropy follows a Page curve. This confirms our previous result [1], which was obtained by directly calculating the thermodynamic entropy of radiation at infinity. We also investigate the presence of a possible island in these systems, and find that it does not seem to play a role in contributing to the generalized black hole entropy.