Cosmic microwave background overview

Abstract

The goal of cosmic microwave background (CMB) and large scale structure (LSS) research is to determine the cosmological parameters that define how structure arose in the universe. These include: early universe parameters associated with fluctuation generation, such as their statistics, the amplitude and shape of primordial power spectra, and the topology of space to the extent that this is accessible; the densities of the various species present, baryons, cold and hot dark matter, the vacuum, as well as the overall mean curvature of space. Current CMB and LSS data provide strong support for the gravitational instability theory, rule out cosmic explosions as a dominant source of LSS, suggest that there was a long period in which hydrogen was recombined between the redshift of photon decoupling and re-ionization associated with early object formation, and are consistent with inflation-based expectations. For example, for inflation-based Gaussian fluctuations in a tilted CDM sequence, the slope of the initial spectrum is within about 5% of the (preferred) scale invariant form both when just the CMB data are used, and when it is combined with LSS data; with both, a nonzero value of is strongly preferred. The corresponding oCDM tilted open sequence prefers , but is overall less likely than the flat sequence. Forecasts of future balloon and satellite experiments predict percent-level accuracy will be attainable among a large fraction of the 10+ parameters characterizing the cosmic structure formation theory.