Super-radiance and flux conservation

Abstract

The theoretical foundations of the phenomenon known as super-radiance still continues to attract considerable attention. Despite many valiant attempts at pedagogically clear presentations, the effect nevertheless still continues to generate some significant confusion. Part of the confusion arises from the fact that super-radiance in a quantum field theory [QFT] context is not the same as super-radiance (super-fluorescence) in some condensed matter contexts; part of the confusion arises from traditional but sometimes awkward normalization conventions, and part is due to sometimes unnecessary confusion between fluxes and probabilities. We shall argue that the key point underlying the effect is flux conservation, (and, in the presence of dissipation, a controlled amount of flux non-conservation), and that attempting to phrase things in terms of reflection and transmission probabilities only works in the absence of super-radiance. To help clarify the situation we present a simple exactly solvable toy model exhibiting both super-radiance and damping.

V1: 8 pages; no figures; V2: 6 references added, no physics changes, now 9 pages

References in corpus (5)

• Instability of the massive Klein-Gordon field on the Kerr spacetime
• `Hidden' Symmetries of Higher Dimensional Rotating Black Holes
• Greybody Factors for Brane Scalar Fields in a Rotating Black-Hole Background
• Scalar Emission in the Bulk in a Rotating Black Hole Background
• Normal Modes, Quasi-normal Modes and Super-radiant Modes for Scalar Fields in Kerr anti-de Sitter Spacetime