Entanglement islands, fuzzballs and stretched horizons

TL;DR

This paper investigates how the island prescription applies to fuzzball-inspired black hole models, revealing conditions under which entanglement islands form or vanish, with implications for the information paradox.

Contribution

It extends the island analysis to fuzzball models, including higher dimensions and stringy geometries, highlighting the dependence on boundary conditions and geometry.

Findings

Boundary conditions influence island existence.

Blinking islands can lead to information paradox.

Island formation depends on geometric features near the cap.

Abstract

We study the implementation of the island prescription in fuzzball-inspired models of black holes. As a simplified setup, we model a fuzzball by replacing the event horizon with a reflecting boundary (stretched horizon). In the framework of two-dimensional model with such boundary, we analyze the dynamics of entanglement entropy. We find that the presence of the boundary modifies the behavior of the island saddle, and for a range of parameter values we observe the effect of blinking island found in arXiv:2311.16244 which inevitably leads to the analogue of information paradox. We then extend the analysis to higher dimensions, incorporating both bulk and boundary contributions to the generalized entropy. The existence of island solutions is found to depend sensitively on the boundary conditions and the position of the stretched horizon, naturally leading to the absence of entanglement islands for a wide range of parameters. Finally, we consider more "realistic" stringy fuzzball geometries, including superstrata and bubbling solutions, and estimate whether island solutions can arise in these backgrounds. The results indicate that the existence of islands depends on the behavior of the geometric area near the cap, and is not guaranteed in general.