EVOLUTION OF COSMIC-STRING CONFIGURATIONS

We extend and develop our previous work on the evolution of a network of cosmic strings. The new treatment is based on an analysis of the pr obability distribution of the end-to-end distance, or extension, of a randomly chosen segment of left-moving string of given length. The des cription involves three distinct length scabs: xi, related to the over all string density, xi; the persistence length along the string, and z eta, describing the small-scale structure, which is an important featu re of the numerical simulations that have been done of this problem. A n evolution equation is derived describing how the distribution develo ps in time due to the combined effects of the universal expansion, of intercommuting and loop formation, and of gravitational radiation. Wit h plausible assumptions about the unknown parameters in the model, we confirm the conclusions of our previous study that if gravitational ra diation and small-scale structure effects ace neglected the two domina nt length scales both scale in proportion to the horizon size. When th e extra effects are included, we find that while xi and ($) over bar x i grow, zeta initially does not. Eventually, however, it does appear t o scale, at a much lower level, due to the effects of gravitational ba ck reaction.