Extending and calibrating the velocity dependent one-scale model for cosmic strings with one thousand field theory simulations

Abstract

Understanding the evolution and cosmological consequences of topological defect networks requires a combination of analytic modeling and numerical simulations. The canonical analytic model for defect network evolution is the Velocity-dependent One-Scale (VOS) model. For the case of cosmic strings, this has so far been calibrated using small numbers of Goto-Nambu and field theory simulations, in the radiation and matter eras, as well as in Minkowski spacetime. But the model is only as good as the available simulations, and it should be extended as further simulations become available. In previous work we presented a General Purpose Graphics Processing Unit implementation of the evolution of cosmological domain wall networks, and used it to obtain an improved VOS model for domain walls. Here we continue this effort, exploiting a more recent analogous code for local Abelian-Higgs string networks. The significant gains in speed afforded by this code enabled us to carry out 1032 field theory simulations of $512^3$ size, with 43 different expansion rates. This detailed exploration of the effects of the expansion rate on the network properties in turn enables a statistical separation of various dynamical processes affecting the evolution of the network. We thus extend and accurately calibrate the VOS model for cosmic strings, including separate terms for energy losses due to loop production and scalar/gauge radiation. By comparing this newly calibrated VOS model with the analogous one for domain walls we quantitatively show that energy loss mechanisms are different for the two types of defects.