Cosmic Strings - Dead Again?

I report on recent numerical simulations of the simplest field theory with cosmic string solutions, the Abelian Higgs model. We find that random networks of string quickly converge to a scaling solution in which the network scale length $ξ$ increases linearly with time. There are very few loops with sizes less than $ξ$, and the strings are smooth, showing no signs of ``small scale structure''. We claim that particle production is the dominant energy-loss mechanism, not gravitational radiation as previously thought. For strings in Grand Unified Models, stringent constraints can be placed from cosmic ray observations on the string tension $μ$: we estimate $Gμ< 10^{-9}$, three orders of magnitude lower than the constraint from Cosmic Microwave Background fluctuations.

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