Periodic Gravitational Waves From Small Cosmic String Loops

TL;DR

This paper investigates the potential for detecting periodic gravitational waves emitted by small, relativistic cosmic string loops within the LIGO frequency band, highlighting the conditions under which such signals could be observed.

Contribution

It introduces a model for gravitational wave emission from small, high-velocity cosmic string loops and assesses their detectability with current gravitational wave detectors.

Findings

LIGO can detect gravitational waves from cosmic string loops with specific tensions.

Detection probability for 10-hour searches is approximately 10^{-4}.

Higher detection chances exist with lower reconnection probabilities and longer observation times.

Abstract

We consider a population of small, high-velocity cosmic string loops. We assume the typical length of these loops is determined by the gravitational radiation scale and use the results of \cite{Polchinski:2007rg} which pointed out their highly relativistic nature. A study of the gravitational wave emission from such a population is carried out. The large Lorentz boost involved causes the lowest harmonics of the loops to fall within the frequency band of the LIGO detector. Due to this feature the gravitational waves emitted by such loops can be detected in a periodic search rather than in burst or stochastic analysis. It is shown that, for interesting values of the string tension ($10^{-10}\lsim G\mu\lsim 10^{-8}$) the detector can observe loops at reasonably high redshifts and that detection is, in principle, possible. We compute the number of expected observations produced by such a process. For a 10 hour search we find that this number is of order $O(10^{-4})$. This is a consequence of the low effective number density of the loops traveling along the line of sight. However, small probabilities of reconnection and longer observation times can improve the result.