Numerical Simulations of String Networks in the Abelian-Higgs Model

We present the results of a field theory simulation of networks of strings in the Abelian-Higgs model. From a random initial configuration the resulting vortex tangle approaches a self-similar regime in which the length density of lines of zeros of $\phi$ reduces as $t^{-2\mathrm{}}$. The network loses energy directly into scalar and gauge radiations supporting a recent claim that particle production, not gravitational radiation, is the dominant energy loss mechanism for cosmic strings. This means that cosmic strings in grand unified theories 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.