REIONIZATION AND COSMIC MICROWAVE ANISOTROPIES

The effects of reionization, occurring after standard recombination in cold dark matter-dominated models, on cosmic microwave background (CM B) anisotropies are investigated. Late-time reionization reduces the C MB anisotropies, in particular, on degree scales. It is found that con straints on cold dark matter-dominated models from the highest frequen cy channel of the 9-point South Pole data are significantly relaxed fo r models which are consistent with big bang nucleosynthesis if reioniz ation is assumed to have occurred by redshift approximately 20.