The Physics of Microwave Background Anisotropies

Cosmic microwave background anisotropies provide a vast amount of cosmological information. Their full physical content and detailed structure can be understood in a simple and intuitive fashion through a systematic investigation of the individual mechanisms for anisotropy formation.

The theoretical basis for the prediction of anisotropies in the cosmic microwave background is very well developed. Very low amplitude density and temperature perturbations produce small gravitational effects, leading to an anisotropy that is a combination of temperature fluctuations at the surface of last scattering and gravitational redshifts both at last scattering and along the path to the observer. All of the primary anisotropy can be handled by linear perturbation theor...

The cosmic microwave background (CMB), the relic radiation from the early Universe, offers a unique window into both primordial conditions and the intervening large-scale structure (LSS) it traverses. Interactions between CMB photons and the evolving Universe imprint secondary anisotropies -- modifications to the CMB's intensity and polarization caused by gravitational effects and scattering processes. These anisotropies serve as a powerful probe of fundamental physics while ...

The physics of the origin and evolution of CMB anisotropies is described. I explain the idea and status of cosmic parameter estimation and follow it up with critical comments on its dependence on model assumptions and initial conditions.

The observed structures in the universe are thought to have arisen from gravitational instability acting on small fluctuations generated in the early universe. These spatial fluctuations are imprinted on the CMBR as angular anisotropies. The physics which connects initial fluctuations in the early universe to the observed anisotropies is fairly well understood, since for most part it involves linear perturbation theory. This makes CMBR anisotropies one of the cleanest probes ...

This article is a written and modified version of a talk presented at the conference `A Century of Cosmology' held at San Servolo, Venice, Italy, in August 2007. The talk focuses on some of the cosmology history leading to the discovery and exploitation of Cosmic Microwave Background (CMB) Radiation anisotropies. We have made tremendous advances first in the development of the techniques to observe these anisotropies and in observing and interpreting them to extract their con...

These lecture notes form a primer on the theory of cosmic microwave background (CMB) anisotropy formation. With emphasis on conceptual aspects rather than technical issues, we examine the physical foundations of anisotropy evolution in relativistic kinetic and perturbation theory as well as the manifestation of these principles in primary and secondary anisotropies. We discuss gauge choice and gauge invariance and their use in understanding the CMB. Acoustic, gravitational re...

The study of anisotropies in the Cosmic Microwave Background radiation is progressing at a phenomenal rate, both experimentally and theoretically. These anisotropies can teach us an enormous amount about the way that fluctuations were generated and the way they subsequently evolved into the clustered galaxies which are observed today. In particular, on sub-degree scales the rich structure in the anisotropy spectrum is the consequence of gravity-driven acoustic oscillations oc...

We summarize the theoretical and observational status of the study of the Cosmic Microwave Background radiation. Its thermodynamic spectrum is a robust prediction of the Hot Big Bang cosmology and has been confirmed observationally. There are now 76 observations of Cosmic Microwave Background anisotropy, which we present in a table with references. We discuss the theoretical origins of these anisotropies and explain the standard jargon associated with their observation.

A compact overview of the status of CMB anisotropy results and their cosmological interpretation up until the end of 2005. Sections headings: Introduction; Description of CMB Anisotropies; Cosmological Parameters; Physics of Anisotropies; Current Anisotropy Data; CMB Polarization; Complications; Constraints on Cosmologies; Particle Physics Constraints; Fundamental Lessons; and Future Directions.