MICROWAVE BACKGROUND ANISOTROPIES FROM SCALING SEED PERTURBATIONS

We study microwave background anisotropies induced by scaling seed per turbations in a universe dominated by cold dark matter. Using a gauge- invariant linear perturbation analysis, we solve the perturbation equa tions on super-horizon scales, for CMB anisotropies triggered by gener ic gravitational seeds. We find that perturbations induced by seeds-un der very mild restrictions-are nearly isocurvature. Thus, compensation , which is mainly the consequence of physically sensible initial condi tions, is very generic. We then restrict our study to the case of scal ing sources, motivated by global scalar fields. We parametrize the ene rgy-momentum tensor of the source by ''seed functions'' and calculate the Sachs-Wolfe and acoustic contributions to the CMB anisotropies. We discuss the dependence of the anisotropy spectrum on the parameters o f the model considered. Even within the restricted class of models inv estigated in this work, we find a surprising variety of results for th e position and height of the first acoustic peak as well as for the ov erall amplitude. In particular, for certain choices of parameters, the spectrum resembles very much the well known adiabatic inflationary sp ectrum, whereas for others. the position of the first acoustic peak is significantly shifted towards smaller angular scales. [S0556-2821(97) 03420-6].