Effect of Reconnection Probability on Cosmic (Super)string Network Density

Abstract

We perform numerical simulations of cosmic string evolution with intercommuting probability $P$ in the range $5\times 10^{-3}\le P\le 1$, both in the matter and radiation eras, using a modified version of the Allen-Shellard code. We find that the dependence of the scaling density on $P$ is significantly different than the suggested $\rho\propto P^{-1}$ form. In particular, for probabilities greater than $P\simeq 0.1$, $\rho(1/P)$ is approximately flat, but for $P$ less than this value it is well-fitted by a power-law with exponent $0.6^{+0.15}_{-0.12}$. This shows that the enhancement of string densities due to a small intercommuting probability is much less prominent than initially anticipated. We interpret the flat part of $\rho(1/P)$ in terms of multiple opportunities for string reconnections during one crossing time, due to small-scale wiggles. We also propose a two-scale model incorporating the key physical mechanisms, which satisfactorily fits our results over the whole range of $P$ covered by the simulations.