Minimal Microwave Anisotropy from Perturbations Induced at Late Times
Abstract
Aside from primordial gravitational instability of the cosmological fluid, various mechanisms have been proposed to generate largescale structure at relatively late times, including, e.g., "latetime" cosmological phase transitions. In these scenarios, it is envisioned that the universe is nearly homogeneous at the time of last scattering and that perturbations grow rapidly sometimes after the primordial plasma recombines. On this basis, it was suggested that large inhomogeneities could be generated while leaving relatively little imprint on the cosmic microwave background (MBR) anisotropy. In this paper, we calculate the minimal anisotropies possible in any "latetime" scenario for structure formation, given the level of inhomogeneity observed at present. Since the growth of the inhomogeneity involves timevarying gravitational fields, these scenarios inevitably generate significant MBR anisotropy via the SachsWolfe effect. Moreover, we show that the largeangle MBR anisotropy produced by the rapid postrecombination growth of inhomogeneity is generally greater than that produced by the same inhomogeneity grown via gravitational instability. In "realistic" scenarios one can decrease the anisotropy compared to models with primordial adiabatic fluctuations, but only on very small angular scales. The value of any particular measure of the anisotropy can be made small in latetime models, but only by making the timedependence of the gravitational field sufficiently "pathological".
 Publication:

The Astrophysical Journal
 Pub Date:
 January 1994
 DOI:
 10.1086/173538
 arXiv:
 arXiv:astroph/9301011
 Bibcode:
 1994ApJ...420....9J
 Keywords:

 Anisotropy;
 Gravitational Fields;
 Microwaves;
 Perturbation;
 Phase Transformations;
 Cosmology;
 Time Dependence;
 Universe;
 Astrophysics;
 COSMOLOGY: COSMIC MICROWAVE BACKGROUND;
 COSMOLOGY: LARGESCALE STRUCTURE OF UNIVERSE;
 Astrophysics
 EPrint:
 Plain TeX, 25 pages, 6 Figures available on request