Type I Abelian Higgs strings: evolution and cosmic microwave background constraints

We present results from the first simulations of networks of Type I Abelian Higgs cosmic strings to include both matter and radiation eras and Cosmic Microwave Background (CMB) constraints. In Type I strings, the string tension is a slowly decreasing function of the ratio of the scalar and gauge mass-squared,ß. We find that the mean string separation shows no dependence on ß, and that the energy-momentum tensor correlators decrease approximately in proportion to the square of the string tension, with additional O(1) correction factors which asymptote to constants below ß?0.01. Strings in models with low self-couplings can therefore satisfy current CMB bounds at higher symmetry-breaking scales. This is particularly relevant for models where the gauge symmetry is broken in a supersymmetric flat direction, for which the effective self-coupling can be extremely small. If our results can be extrapolated to ß?10-15,even strings formed at 10-16 GeV (approximately the grand unification scale in supersymmetric extensions of the Standard Model) can be compatible with CMB constraints.