Toward understanding CMB anisotropies and their implications

Abstract

Working toward a model-independent understanding of cosmic microwave background (CMB) anisotropies and their significance, we undertake a comprehensive and self-contained study of scalar perturbation theory. Initial conditions, evolution, thermal history, matter content, background dynamics, and geometry all play a role in determining the anisotropy. By employing analytic techniques to illuminate the numerical results, we are able to separate and identify each contribution. We thus bring out the nature of the total Sachs-Wolfe effect, acoustic oscillations, diffusion damping, Doppler shifts, and reionization, as well as their particular manifestation in a critical curvature, or cosmological-constant-dominated universe. By studying the full angular and spatial content of the resultant fluctuations, we isolate the signature of these effects from the dependence on initial conditions. Whereas structure in the Sachs-Wolfe anisotropy depends strongly on the underlying power spectra, the acoustic oscillations provide features which are nearly model independent. This may allow for future determination of the matter content of the Universe as well as the adiabatic and/or isocurvature nature of the initial fluctuations.