The 21cm Signature of a Cosmic String Loop

TL;DR

This paper predicts that cosmic string loops create distinctive 21cm brightness temperature signals at high redshifts, which could be detected by upcoming surveys, providing a new way to probe cosmic strings.

Contribution

It calculates the amplitude and shape of 21cm signals caused by cosmic string loops, highlighting their potential observability and distinctive features.

Findings

String loops produce elliptical 21cm emission regions.

Brightness temperature excess can reach up to 1 K.

Angular size of signals is about 0.1 degree.

Abstract

Cosmic string loops lead to nonlinear baryon overdensities at early times, even before the time which in the standard LCDM model corresponds to the time of reionization. These overdense structures lead to signals in 21cm redshift surveys at large redshifts. In this paper, we calculate the amplitude and shape of the string loop-induced 21cm brightness temperature. We find that a string loop leads to a roughly elliptical region in redshift space with extra 21cm emission. The excess brightness temperature for strings with a tension close to the current upper bound can be as high as 1 degree K for string loops generated at early cosmological times (times comparable to the time of equal matter and radiation) and observed at a redshift of z + 1 = 30. The angular extent of these predicted "bright spots" is of the order 0.1 degree for a value of the string tension equal to the current upper bound. These signals should be detectable in upcoming high redshift 21cm surveys.