Wandering in the Background: A CMB Explorer

TL;DR

This paper develops a comprehensive theoretical framework to analyze distortions and anisotropies in the cosmic microwave background, providing insights into the universe's composition, expansion, and structure formation.

Contribution

It introduces a model-independent approach using relativistic kinetic and perturbation theory to study CMB distortions and anisotropies in various cosmological models.

Findings

Anisotropies are primarily governed by Compton scattering and gravitational coupling.

The framework allows analysis of open, critical, and cosmological constant universes.

Results include predictions for anisotropy patterns under different initial conditions.

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.