968 research outputs found
The growth of linear perturbations in generic defect models for structure formation
We study the growth of linear perturbations induced by a generic causal
scaling source as a function of the cosmological parameters ,
and . We show that for wavenumbers k \gsim 0.01 h/Mpc the
spectrum of density and velocity perturbations scale in a similar way to that
found in inflationary models with primordial perturbations. We show that this
result is independent of the more or less incoherent nature of the source, the
small scale power spectrum of the source and of deviations from scaling which
naturally occur at late times if .Comment: 4 pages, 2 figure
The cluster abundance in cosmic string models for structure formation
We use the present observed number density of large X-ray clusters to
constrain the amplitude of matter density perturbations induced by cosmic
strings on the scale of Mpc (), in both open cosmologies
and flat models with a non-zero cosmological constant. We find a slightly lower
value of than that obtained in the context of primordial Gaussian
fluctuations generated during inflation. This lower normalization of
results from the mild non-Gaussianity on cluster scales, where the one point
probability distribution function is well approximated by a
distribution. We use our estimate of to constrain the string linear
energy density and show that it is consistent with the COBE
normalization.Comment: 5 pages, 2 figure
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