Vacuum polarization throughout general subtracted black hole spacetimes

TL;DR

This paper derives an analytical expression for the vacuum polarization of a massless scalar field in a rotating, charged black hole spacetime with subtracted geometry, revealing divergence at the inner horizon.

Contribution

It provides the first analytical, spacetime-wide vacuum polarization expression for rotating, charged black holes with subtracted geometry, extending previous horizon-only results.

Findings

Vacuum polarization diverges at the inner horizon.

Quantum state cannot be extended beyond the inner horizon.

Analytical expression valid for arbitrary rotation and charge.

Abstract

We compute the vacuum polarization of a massless minimally co pled scalar field in a background given by a black hole with subtracted geometry. Extending previous results for the horizon of rotating black holes with no charge, we obtain an analytical expression for the vacuum polarization that is valid throughout the spacetime and for arbitrary rotation and charge parameters. The vacuum polarization diverges at the inner horizon and the quantum state cannot be extended to the inside of it.