Superradiant scattering of dispersive fields

TL;DR

This paper investigates how dispersive modifications to wave equations influence superradiant scattering, demonstrating amplification effects and deviations in spectra through simple models, with implications for analogue gravity experiments.

Contribution

It introduces a detailed analysis of superradiance in dispersive fields, highlighting the impact of extra degrees of freedom and medium motion on amplification phenomena.

Findings

Dispersive effects can enhance superradiant amplification.

Low-frequency waves can be amplified during scattering.

Superradiance occurs even in moving media with dispersive fields.

Abstract

Motivated by analogue models of classical and quantum field theory in curved spacetimes and their recent experimental realizations, we consider wave scattering processes of dispersive fields exhibiting two extra degrees of freedom. In particular, we investigate how standard superradiant scattering processes are affected by subluminal or superluminal modifications of the dispersion relation. We analyze simple 1-dimensional toy-models based on fourth-order corrections to the standard second order wave equation and show that low-frequency waves impinging on generic scattering potentials can be amplified during the process. In specific cases, by assuming a simple step potential, we determine quantitatively the deviations in the amplification spectrum that arise due to dispersion, and demonstrate that the amplification can be further enhanced due to the presence of extra degrees of freedom. We also consider dispersive scattering processes in which the medium where the scattering takes place is moving with respect to the observer and show that superradiance can also be manifest in such situations.