Superradiance in the Kerr-Taub-NUT spacetime

TL;DR

This paper investigates superradiance phenomena in Kerr-Taub-NUT spacetime, deriving equations for various spin fields and providing analytical results for low-energy scattering, including emission rates and cross sections.

Contribution

It introduces a generalized Teukolsky equation for all spin perturbations in Kerr-Taub-NUT spacetime and analyzes superradiant scattering with new analytical expressions.

Findings

Derived a master equation for all spin fields in Kerr-Taub-NUT spacetime.

Separated equations into angular and radial parts with generalized spheroidal harmonics.

Provided analytical formulas for low-energy emission rates and cross sections.

Abstract

Superradiance is the effect of field waves being amplified during reflection from a charged or rotating black hole. In this paper, we study the low-energy dynamics of super-radiant scattering of massive scalar and massless higher spin field perturbations in a generic axisymmetric stationary Kerr-Taub-NUT (Newman-Unti-Tamburino) spacetime, which represents sources with both gravitomagnetic monopole moment (magnetic mass) and gravitomagnetic dipole moment (angular momentum). We obtain a generalized Teukolsky master equation for all spin perturbation fields. The equations are separated into their angular and radial parts. The angular equations lead to spin-weighted spheroidal harmonic functions that generalize those in Kerr spacetime. We identify an effective spin as a coupling between frequency (or energy) and the NUT parameter. The behaviors of the radial wave function near the horizon and at the infinite boundary are studied. We provide analytical expressions for low-energy observables such as emission rates and cross sections of all massless fields with spin, including scalar, neutrino, electromagnetic, Rarita-Schwinger, and gravitational waves.