Detailed study of defect models for cosmic structure formation

Abstract

We calculate predictions from wide class of `active' models of cosmic structure formation which allows us to scan the space of possible defect models. We calculate the linear cold dark matter power spectrum and Cosmic Microwave Background (CMB) anisotropies over all observable scales using a full linear Einstein-Boltzmann code. Our main result, which has already been reported, points to a serious problem reconciling the observed amplitude of the large-scale galaxy distribution with the COBE normalization. Here, we describe our methods and results in detail. The problem is present for a wide range of defect parameters, which can be used to represent potential differences among defect models, as well as possible systematic numerical errors. We explicitly examine the impact of varying the defect model parameters and we show how the results substantiate these conclusions. The standard scaling defect models are in serious conflict with the current data, and we show how attempts to resolve the problem by considering non-scaling defects or modified stress-energy components would require radical departures from what has become the standard picture.