Survival of pq-superstrings in field theory simulations

Abstract

We perform large-scale field theoretical simulations in expanding universe to characterize a network of strings that can form composed bound states. The network consists of two copies of Abelian Higgs strings (which we label p and q, respectively) coupled via a potential term to give pq bound states. The simulations are performed using two different kinds of initial conditions: the first one with a network of p- and q-strings, and the second one with a network of q- and pq-strings. This way, we start from two opposite situations: one with no initial pq-strings, and one with a large initial number of pq-strings. We find that in both cases the system scales, and in both cases the system prefers to have a low fraction of pq-strings. This is somewhat surprising in the case for the second type of conditions, showing that the unzipping mechanism is very efficient. We also find hints that both initial conditions tend to asymptote to a common configuration, though we would need a larger dynamical range to confirm it. The average velocities of the different types of strings in the network have also been explored for the first time.