Can cosmic strings generate large-scale streaming velocities?

Abstract

A detailed calculation is presented of the generation of large-scale streaming velocities by nonsuperconducting cosmic strings. Both semianalytic methods and Monte Carlo simulations are used and yield good agreement. The calculations include an exact treatment of the transition from a radiation-dominated to a matter-dominated universe, a model of loop correlations, and loop-peculiar velocities. The results for the Turok and Brandenberger string parameters in a universe with cold dark matter are the following: (1) uncorrelated loops produce a rms streaming velocity of 71 km s^-1^ averaged over a sphere of radius 60 h^-1^ Mpc; (2) loop correlations increase this velocity to ~107 km s^-1^; (3) loop velocities have little effect; and (4) although the distribution of streaming velocities is broader than a Gaussian, the probability of generating a large-scale streaming velocity as large as the 599 +/- 104 km s^-1^ reported by Dressler et al. is extremely small. Hot dark matter may increase the predicted velocities by a factor of ~3. Cosmic strings and cold dark matter are in apparent conflict with observations, but with hot dark matter, cosmic strings offer a hope of explaining the reported large-scale streaming velocities.