Entropy Perturbations due to Cosmic Strings
  We examine variations in the equation of state of the cosmic string portion of the cosmological fluid which lead to perturbations of the background matter density. These fluctuations in the equation of state are due to variations in the local density of cosmic string loops and gravitational radiation. Constructing a crude model of the distribution of entropy perturbations, we obtain the resulting fluctuation spectrum using a gauge-invariant formalism. We compute the resulting cosmic microwave background anisotropy, and estimate the effect of these perturbations on the cosmic string structure formation scenario. 
Pedro Avelino and Robert Caldwell (University of Cambridge - DAMTP)