GRAVITATIONAL RADIATION FROM REALISTIC COSMIC STRING LOOPS

TL;DR

This study analyzes gravitational wave emission from realistic cosmic string loops, finding most loops radiate minimally and establishing a lower bound on radiation rates, with implications for cosmic string detection.

Contribution

It provides the first comprehensive numerical analysis of gravitational radiation from a large set of realistic cosmic string loops, identifying a lower bound on radiation rates.

Findings

Most loops do not radiate significant spatial momentum.

The distribution of radiation rates peaks at $ ext{45-55}$, with no loops below 40.

A conjectured minimal radiation rate of approximately 39.003.

Abstract

We examine the rates at which energy and momentum are radiated into gravitational waves by a large set of realistic cosmic string loops. The string loops are generated by numerically evolving parent loops with different initial conditions forward in time until they self-intersect, fragmenting into two child loops. The fragmentation of the child loops is followed recursively until only non-self-intersecting loops remain. The properties of the final non-self-intersecting loops are found to be independent of the initial conditions of the parent loops. We have calculated the radiated energy and momentum for a total of 11,625 stable child loops. We find that the majority of the final loops do not radiate significant amounts of spatial momentum. The velocity gained due to the rocket effect is typically small compared to the center-of-mass velocity of the fragmented loops. The distribution of gravitational radiation rates in the center of mass frame of the loops, $\gamma^0 \equiv (G\mu^2)^{-1} \Delta E/\Delta \tau$, is strongly peaked in the range $\gamma^0=45-55$, however there are no loops found with $\gamma^0 < 40$. Because the radiated spatial momentum is small, the distribution of gravitational radiation rates appears roughly the same in any reference frame. We conjecture that in the center-of-mass frame there is a lower bound $\gamma^0_{\rm min}>0$ for the radiation rate from cosmic string loops. In a second conjecture, we identify a candidate for the loop with the minimal radiation rate and suggest that $\gamma^0_{\rm min}\cong 39.003$.