A Little Excitement Across the Horizon

TL;DR

This paper numerically investigates the transition probabilities of an Unruh-DeWitt detector in Schwarzschild spacetime, revealing state-dependent behaviors near the horizon and a novel extremum linked to angular momentum effects.

Contribution

It provides the first detailed numerical analysis of detector transitions in different quantum states around a black hole horizon, highlighting new physical insights.

Findings

Transition probability has a local extremum near the horizon in Hartle-Hawking and Unruh states.

In Boulware state, the transition probability decreases approaching the horizon.

The near-horizon extremum is caused by angular momentum superpositions.

Abstract

We analyse numerically the transitions in an Unruh-DeWitt detector, coupled linearly to a massless scalar field, in radial infall in (3+1)-dimensional Schwarzschild spacetime. In the Hartle-Hawking and Unruh states, the transition probability attains a small local extremum near the horizon-crossing and is then moderately enhanced on approaching the singularity. In the Boulware state, the transition probability drops on approaching the horizon. The unexpected near-horizon extremum arises numerically from angular momentum superpositions, with a deeper physical explanation to be found.