Wandering in the Background: A CMB Explorer

Abstract

We develop and examine the principles governing the formation of distortions in the cosmic microwave background. Distortions in the frequency or spectral distribution of the background probe the thermal history of the universe whereas those in the angular temperature distribution probe its dynamics and geometry. Stressing model independent results, we show how the microwave background can be used to extract information on the mass density, vacuum density, baryon content, radiation content, expansion rate and some aspects of structure formation in the universe. To address these issues, we systematically develop relativistic kinetic and perturbation theory addressing issues such as fluctuation representation, or gauge, normal mode analysis in an open geometry, and second order effects. Through analytic and numerical results, we construct anisotropies in a critical, open, or cosmological constant universe with adiabatic and/or isocurvature initial conditions allowing for possible early reionization. We find that anisotropy formation is a simple process governed by the Compton scattering of photons and electrons and their gravitational coupling to the other particle species in the universe.