Anastasia N. Zueva | Searcharxiv

arXiv2026

Entanglement islands, fuzzballs and stretched horizons

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.

hep-th↗

arXiv2025

Spectral form factors for curved spacetimes with horizon

The spectral form factor is believed to exhibit a special type of behavior called ``dip-ramp-plateau'' in chaotic quantum systems that originates from random matrix theory. This suggests that the shape of the spectral form factor could serve as an indicator of chaos in various quantum systems. It has been shown recently that the dip-ramp-plateau structure appears in the spectral form factor when the normal modes of a massless scalar field theory in the brick-wall model of the BTZ black hole are treated as eigenvalues of a quantum Hamiltonian. At the same time, the level spacing distribution of these normal modes differs from that associated with random matrix theory ensembles. In this paper, we extend the results for BTZ background to the case of non-zero mass of the field, study the generalized spectral form-factor, and consider the same context for another non-trivial background -- de Sitter space. We compare the generalized spectral form factor for simple integrable quantum systems and for backgrounds with a horizon to the behavior predicted by random matrix theory. As a result, we confirm that BTZ and de Sitter brick-wall models are highly distinct integrable systems that exhibit the dip-ramp-plateau structure of the SFF but differ in the structure of the three-level generalized spectral form factor from the one predicted by random matrix theory. This raises the question on whether the DRP structure is an indicator of what is known as quantum chaos.

hep-th↗