Journal
PHYSICAL REVIEW D
Volume 93, Issue 4, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevD.93.043013
Keywords
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Funding
- University of California Office of the President Multicampus Research Programs and Initiatives [MR-15-328388]
- NSF CAREER [1352519]
- NSF AST Grant [1129258, 1440343]
- NASA - Space Telescope Science Institute [HST-HF2-51363.001-A]
- NASA [NAS5-26555]
- European Research Council under ERC [638743-FIRSTDAWN]
- European Union's Seventh Framework Programme FP7-PEOPLE-CIG [321933-21ALPHA]
- STFC consolidated Grant [ST/K001051/1]
- ERC [259505]
- Miller Institute for Basic Research in Science at the University of California, Berkeley
- Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]
- STFC [ST/K001051/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/K001051/1] Funding Source: researchfish
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Amongst standard model parameters that are constrained by cosmic microwave background (CMB) observations, the optical depth tau stands out as a nuisance parameter. While tau provides some crude limits on reionization, it also degrades constraints on other cosmological parameters. Here we explore how 21 cm cosmology-as a direct probe of reionization-can be used to independently predict tau in an effort to improve CMB parameter constraints. We develop two complementary schemes for doing so. The first uses 21 cm power spectrum observations in conjunction with semianalytic simulations to predict tau. The other uses global 21 cm measurements to directly constrain low redshift (post-reheating) contributions to tau in a relatively model-independent way. Forecasting the performance of the upcoming hydrogen epoch of reionization array, we find that significant reductions in the errors on tau can be achieved. These results are particularly effective at breaking the CMB degeneracy between tau and the amplitude of the primordial fluctuation spectrum A(s), with errors on ln(10(10)A(s)) reduced by up to a factor of 4. Stage 4 CMB constraints on the neutrino mass sum are also improved, with errors potentially reduced to 12 meV regardless of whether CMB experiments can precisely measure the reionization bump in polarization power spectra. Observations of the 21 cm line are therefore capable of improving not only our understanding of reionization astrophysics, but also of cosmology in general.
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