ACCRETION OF COLD AND HOT DARK-MATTER ONTO COSMIC-STRING FILAMENTS

The Zeldovich approximation is applied to study the accretion of hot a nd cold dark matter onto moving long strings. It is assumed that such defects carry a substantial amount of small-scale structure, thereby a cting gravitationally as a Newtonian line source whose effects dominat e the velocity perturbations. Analytical expressions for the turnaroun d surfaces are derived and the mass inside of these surfaces is calcul ated. Estimates are given for the redshift dependence of Omega(nl), th e fraction of mass in nonlinear objects. Depending on parameters, it i s possible to obtain Omega(nl)=1 at the present time. Even with hot da rk matter, the first nonlinear filamentary structures form at a redshi ft close to 100, and there is sufficient nonlinear mass to explain the observed abundance of high redshift quasars and damped Lyman alpha sy stems. These results imply that moving strings with small-scale struct ure are the most efficient seeds to produce massive nonlinear objects in the cosmic string model.