Delayed Recombination and Cosmic Parameters
  Current cosmological constraints from Cosmic Microwave Background (CMB) anisotropies are typically derived assuming a standard recombination scheme, however additional resonance and ionizing radiation sources can delay recombination, altering the cosmic ionization history and the cosmological inferences drawn from CMB data. We show that for recent observations of CMB anisotropy, from the Wilkinson Microwave Anisotropy Probe satellite mission 5-year survey (WMAP5) and from the ACBAR experiment, additional resonance radiation is nearly degenerate with variations in the spectral index, n_s, and has a marked effect on uncertainties in constraints on the Hubble constant, age of the universe, curvature and the upper bound on the neutrino mass. When a modified recombination scheme is considered, the redshift of recombination is constrained to z_*=1078\pm11, with uncertainties in the measurement weaker by one order of magnitude than those obtained under the assumption of standard recombination while constraints on the shift parameter are shifted by 1-sigma to R=1.734\pm0.028. Although delayed recombination limits the precision of parameter estimation from the WMAP satellite, we demonstrate that this should not be the case for future, smaller angular scales measurements, such as those by the Planck satellite mission. 
Silvia Galli, Rachel Bean, Alessandro Melchiorri and Joseph Silk