We present the results of a field theory simulation of networks of strings in the Abelian Higgs model. Starting from a random initial configuration we show that the resulting vortex tangle approaches a self-similar regime in which the length density of lines of zeros of $\phi$ reduces as $t^{-2}$. We demonstrate that the network loses energy through processes operating at the string width. These results support a recent claim that particle production, and not gravitational radiation, is the dominant energy loss mechanism for cosmic strings. This means that GUT-scale cosmic strings are severely constrained by high energy cosmic ray fluxes: either they are ruled out, or an implausibly small fraction of their energy ends up in quarks and leptons.
Postscript from: Los Alamos, Zaragoza, Trieste, Paris, Augsburg, Southampton, Moscow.
We investigate the dynamics of second order phase transitions in two dimensions, breaking a gauged U(1) symmetry. Using numerical simulations, we show that the density of topological defects formed scales with the quench timescale $\tau_Q$ as $n \sim \tau_Q^{-1/2}$ when the dynamics is overdamped at the instant when the freezeout of thermal fluctuations takes place, and $n \sim \tau_Q^{-2/3}$ in the underdamped case. This is predicted by the scenario proposed by one of us [1].
Postscript from: Los Alamos, Zaragoza, Trieste, Paris, Augsburg, Southampton, Moscow.