LARGE-SCALE STRUCTURE FORMATION WITH GLOBAL TOPOLOGICAL DEFECTS

We investigate cosmological structure formation seeded by topological defects which may form during a phase transition in the early Universe . First, we derive a partially new, local, and gauge-invariant system of perturbation equations to treat microwave background and dark matte r fluctuations induced by topological defects or any other type of see ds. We then show that this system is well suited for numerical analysi s of structure formation by applying it to seeds induced by fluctuatio ns of a global scalar field. Our numerical results cover a larger dyna mical range than those covered by previous investigations and are comp lementary to them since we use substantially different methods. The re sulting microwave background fluctuations are compatible with older si mulations. We also obtain a scale-invariant spectrum of fluctuations a lthough with somewhat higher amplitude. On the other hand, our dark ma tter results yield a smaller bias parameter compatible with b similar to 2 on scales of 20h(-1) Mpc in contrast with previous work which yie lded larger bias factors. Our conclusions are thus more positive. Acco rding to the aspects analyzed in this work, global topological defect- induced fluctuations yield viable scenarios of structure formation and do better than standard CDM on large scales.