Delayed Recombination and Cosmic Parameters

TL;DR

This paper investigates how delayed recombination due to additional radiation sources affects cosmological parameter constraints from CMB data, highlighting degeneracies and the importance of considering non-standard recombination in analyses.

Contribution

It introduces a modified recombination scheme and analyzes its impact on cosmological parameter estimation from WMAP5 and ACBAR data.

Findings

Delayed recombination shifts the redshift of recombination to z_*=1078±11.

Uncertainties in cosmological parameters increase when considering non-standard recombination.

Future measurements like Planck can mitigate the limitations caused by delayed recombination.

Abstract

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.