title: Decaying particles and the reionization history of the universe.
abstract: We investigate the possibility that the Universe is significantly reionized by the decay products of heavy particles. The ionization produced by decaying particles implies a high optical depth even if the maximum level of ionization ever produced is low (10(-2)). As a consequence, a high ionization fraction (x approximately equal to 0.5) at high redshifts (z approximately equal to 20) fails to fit the cosmic microwave background (CMB) spectra at l> or =30. Recent CMB data limit the primordial abundance of the decaying particles, favoring long decay times. Other significant sources of reionization are still needed at z approximately equal to 13. The decay process heats up the medium, bringing the expected y distortion to unobservable levels.
authors.affiliation: Physics Department, Princeton University, Princeton, New Jersey 08544, USA. epierpao@princeton.edu
authors.forename: Elena
authors.initials: E
authors.lastname: Pierpaoli