MASSLESS (PSEUDO-)SCALAR SEEDS OF CMB ANISOTROPY

A primordial stochastic background of very weakly coupled massless (ps eudo-)scalars can seed CMB anisotropy, when large-scale Fluctuations o f their stress-tensor re-enter the horizon during the matter-dominated era. A general relation between multipole coefficients of the CMB ani sotropy and the seed's energy spectrum is derived. Magnitude and tilt of the observed anisotropies can be reproduced for the nearly scale-in variant axion spectra that are predicted in a particularly symmetric c lass of string cosmology backgrounds. (C) 1998 Elsevier Science B.V. A ll rights reserved.