Electromagnetic field near cosmic string

TL;DR

This paper derives the electromagnetic Green function near a cosmic string, revealing how the string influences electromagnetic fields through scattering and self-interaction, altering multipole structures and expelling fields locally.

Contribution

It provides the explicit form of the electromagnetic Green function in cosmic string spacetime and analyzes its effects on static sources and field configurations.

Findings

Fields are affected by self-interaction with the string

Distant static fields have altered multipole structures

Fields are expelled from regions near the string

Abstract

The retarded Green function of the electromagnetic field in spacetime of a straight thin cosmic string is found. It splits into a geodesic part (corresponding to the propagation along null rays) and to the field scattered on the string. With help of the Green function the electric and magnetic fields of simple sources are constructed. It is shown that these sources are influenced by the cosmic string through a self-interaction with their field. The distant field of static sources is studied and it is found that it has a different multipole structure than in Minkowski spacetime. On the other hand, the string suppresses the electric and magnetic field of distant sources--the field is expelled from regions near the string.