Superradiance in Stars: Non-equilibrium approach to damping of fields in stellar media

TL;DR

This paper develops a systematic theoretical framework to compute superradiance rates in rotating stars, extending the understanding from black holes to stellar media and enabling analysis of various interactions with bosonic fields.

Contribution

It introduces a novel method combining finite density field theory and worldline formalism to calculate superradiance in stars, which was previously lacking.

Findings

First systematic pipeline for stellar superradiance rates

Applicable to any interaction between bosonic fields and stellar matter

Provides a firm theoretical basis for future observational signatures

Abstract

Superradiance in black holes is well-understood but a general treatment for superradiance in stars has until now been lacking. This is surprising given the ease with which we can observe isolated neutron stars and the array of signatures which would result from stellar superradiance. In this work, we present the first systematic pipeline for computing superradiance rates in rotating stars. Our method can be used with any Lagrangian describing the interaction between the superradiant field and the constituents of the star. Our scheme falls into two parts: firstly we show how field theory at finite density can be used to express the absorption of long wavelength modes into the star in terms of microphsyical scattering processes. This allows us to derive a damped equation of motion for the bosonic field. We then feed this into an effective theory for long wavelengths (the so-called worldline formalism) to describe the amplification of superradiant modes of arbitrary multipole moment for a rapidly rotating star. Our method places stellar superradiance on a firm theoretical footing and allows the calculation of the superradiance rate arising from any interaction between a bosonic field and stellar matter.