Matter accretion by cosmic string loops and wakes.

Abstract

We develop quantative methods for the study of structure formation with cosmic strings in an expanding universe. The gravitational effects of arbitrary string configurations are calculated using linearized gravity. The growth of density fluctuations is then studied using these gravitational forces as a source term in the Zeldovich approximation. We use either the adhesion modification or an N-body tree code to project this fluctuation growth into the nonlinear regime. These methods are applied to specific loop and long string solutions beginning at equal matter and radiation ${\mathit{t}}_{\mathrm{eq}}$ on scales corresponding to about 10 Mpc today (h=0.5). We reproduce analytic results for spherical and planar collapse. We show that these methods are applicable to accretion about closed oscillating loops and in the wakes of moving long strings which possess significant small-scale structure, quantitatively confirming the wiggly string approximation with a renormalized string energy density \ensuremath{\mu}\ifmmode \tilde{}\else \~{}\fi{}. We demonstrate the efficiency of the fragmentation of wakes created by wiggly strings by the present day. These methods are sufficiently computationally efficient to employ in the study of an evolving string network. For the cosmic string scenario, we conclude that reliable quantitative predictions must take into account non-Gaussianity, vorticity generation, and nonlinear fragmentation effects.