A TwoFluid Approximation for Calculating the Cosmic Microwave Background Anisotropies
Abstract
We present a simple, yet accurate approximation for calculating the cosmic microwave background anisotropy power spectrum in adiabatic models. It consists of solving for the evolution of a twofluid model until the epoch of recombination and then integrating over the sources to obtain the CMB anisotropy power spectrum. The approximation is useful both for a physical understanding of CMB anisotropies, as well as for a quantitative analysis of cosmological models. Comparison with exact calculations shows that the accuracy is typically better than 20 percent over a large range of angles and cosmological models, including those with curvature and cosmological constant. Using this approximation we investigate the dependence of the CMB anisotropies on the cosmological parameters. We identify six dimensionless parameters that uniquely determine the anisotropy power spectrum within our approximation. CMB experiments on different angular scales could in principle provide information on all these parameters. In particular, mapping of the Doppler peaks would allow an independent determination of baryon mass density, matter mass density and Hubble constant.
 Publication:

The Astrophysical Journal
 Pub Date:
 November 1994
 DOI:
 10.1086/187601
 arXiv:
 arXiv:astroph/9406050
 Bibcode:
 1994ApJ...435L..87S
 Keywords:

 Anisotropy;
 Background Radiation;
 Baryons;
 Cosmic Rays;
 Cosmology;
 Microwaves;
 Power Spectra;
 Two Fluid Models;
 Adiabatic Equations;
 Approximation;
 Astronomical Models;
 Density (Mass/Volume);
 Evolution (Development);
 Microwave Spectra;
 Recombination Reactions;
 Stellar Radiation;
 Astrophysics;
 COSMOLOGY: THEORY;
 COSMOLOGY: COSMIC MICROWAVE BACKGROUND;
 Astrophysics
 EPrint:
 12 pages, AAS Latex, ApJL, submitted 1994, preprint MITCSR9413