Gravitational Scattering Of Photons Off Cosmic Strings

TL;DR

This paper investigates how cosmic string loops gravitationally scatter photons, causing spectral distortions in the cosmic microwave background that could be detectable, depending on string tension and redshift.

Contribution

It estimates the magnitude of spectral distortions caused by cosmic strings, highlighting their potential observability in cosmological data.

Findings

Spectral distortion scales as (G_N μ)^2 z^2

Distortions could be significant enough for observational detection

Provides a framework for constraining cosmic string properties

Abstract

Photons can gravitationally scatter off a cosmic string loop and gain or lose energy. We consider the spectral distortion induced by cosmic string loops placed in an ambient thermal bath of photons. The fractional deviation from a thermal spectrum caused by cosmic strings is estimated to scale as (G_N \mu)^2 z^2, where G_N is Newton's constant, $\mu$ is the string tension, and z is the cosmological redshift after which spectral distortions can survive. This effect is large enough to potentially be of observational interest.