CONSTRAINTS ON PERTURBATIONS TO THE RECOMBINATION HISTORY FROM MEASUREMENTS OF THE COSMIC MICROWAVE BACKGROUND DAMPING TAIL
- Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON M5S 3H8 (Canada)
The primordial cosmic microwave background at small angular scales is sensitive to the ionization and expansion history of the universe around the time of recombination. This dependence has been exploited to constrain the helium abundance and the effective number of relativistic species. Here we focus on allowed ionization fraction trajectories, x {sub e}(z), by constraining low-order principal components of perturbations to the standard recombination scenario (x {sub e}-eigenmodes) in the circa 2011 South Pole Telescope (SPT), Atacama Cosmology Telescope (ACT), and Wilkinson Microwave Anisotropy Probe seven-year data (WMAP7). Although the trajectories are statistically consistent with the standard recombination, we find that there is a tension similar to that found by varying the helium fraction. As this paper was in press, final SPT and ACT datasets were released and we applied our framework to them: we find that the tension continues, with slightly higher significance, in the new 2012 SPT data, but find no tension with the standard model of recombination in the new 2012 ACT data. We find that the prior probabilities on the eigenamplitudes are substantially influenced by the requirement that x {sub e}-trajectories conserve electron number. We propose requiring a sufficient entropy decrease between posterior and prior marginalized distributions be used as an x {sub e}-mode selection criterion. We find that in the case of the 2011 SPT/ACT+WMAP7 data only two modes are constrainable, but upcoming ACTPol, Planck, and SPTPol data will be able to test more modes and more precisely address the current tension.
- OSTI ID:
- 22167717
- Journal Information:
- Astrophysical Journal, Vol. 764, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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