On the Origin of the Outgoing Black Hole Modes

TL;DR

This paper explores how outgoing black hole modes can originate from ingoing modes through mode conversion, emphasizing the importance of back-reaction and physical cutoffs, with analogies from plasma physics and condensed matter systems.

Contribution

It proposes a mechanism for black hole outgoing modes via mode conversion from ingoing modes, incorporating back-reaction and physical cutoffs, supported by models and analogies.

Findings

Outgoing modes arise from ingoing modes via conversion.

Back-reaction is essential to enable particle creation.

Analogies with plasma physics and condensed matter systems support the mechanism.

Abstract

The question of how to account for the outgoing black hole modes without drawing upon a transplanckian reservoir at the horizon is addressed. It is argued that the outgoing modes must arise via conversion from ingoing modes. It is further argued that the back-reaction must be included to avoid the conclusion that particle creation cannot occur in a strictly stationary background. The process of ``mode conversion" is known in plasma physics by this name and in condensed matter physics as ``Andreev reflection" or ``branch conversion". It is illustrated here in a linear Lorentz non-invariant model introduced by Unruh. The role of interactions and a physical short distance cutoff is then examined in the sonic black hole formed with Helium-II.