Gravitational Wave Scattering on Magnetic Fields

TL;DR

This paper models how gravitational waves convert into electromagnetic waves in magnetic fields, analyzing angular distribution, polarization effects, and potential astrophysical applications like neutron star magnetospheres.

Contribution

It provides a classical electrodynamics framework for gravitational-electromagnetic wave conversion, including polarization and medium effects, extending previous theoretical understanding.

Findings

Dipolar magnetic fields can polarize gravitational wave backgrounds.

Peak electromagnetic emission occurs along the equator in dipolar fields.

Framework includes medium effects for realistic astrophysical environments.

Abstract

The conversion of gravitational to electromagnetic waves in the presence of background magnetic fields is known as the inverse Gertsenshtein effect, analogous to the Primakoff effect for axions. Rephrasing this conversion as a classical electrodynamics problem in the far-field regime of a magnetized region, we derive the angular distribution of the intensity and polarization of the emitted electromagnetic waves. We discuss the interplay of the internal structure of the magnetic field, the polarization of the gravitational wave and the scattering angle, demonstrating for example that a dipolar field can convert an unpolarized stochastic gravitational wave background into polarized electromagnetic emission, with peak emission intensity along the equator. We moreover outline how to incorporate medium effects in this framework, necessary for a realistic 3D description of gravitational wave to photon conversion in the magnetosphere of neutron stars.