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Detecting primordial gravitational waves with circular polarization of the redshifted 21 cm line. II. Forecasts

Mishra, Abhilash and Hirata, Christopher M. (2018) Detecting primordial gravitational waves with circular polarization of the redshifted 21 cm line. II. Forecasts. Physical Review D, 97 (10). Art. No. 103522. ISSN 2470-0010. doi:10.1103/PhysRevD.97.103522.

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In the first paper of this series, we showed that the CMB quadrupole at high redshifts results in a small circular polarization of the emitted 21 cm radiation. In this paper we forecast the sensitivity of future radio experiments to measure the CMB quadrupole during the era of first cosmic light (z ∼ 20). The tomographic measurement of 21 cm circular polarization allows us to construct a 3D remote quadrupole field. Measuring the B-mode component of this remote quadrupole field can be used to put bounds on the tensor-to-scalar ratio r. We make Fisher forecasts for a future Fast Fourier Transform Telescope (FFTT), consisting of an array of dipole antennas in a compact grid configuration, as a function of array size and observation time. We find that a FFTT with a side length of 100 km can achieve σ(r) ∼ 4 × 10^(−3) after ten years of observation and with a sky coverage f_(sky) ∼ 0.7. The forecasts are dependent on the evolution of the Lyman-α flux in the pre-reionization era, that remains observationally unconstrained. Finally, we calculate the typical order of magnitudes for circular polarization foregrounds and comment on their mitigation strategies. We conclude that detection of primordial gravitational waves with 21 cm observations is in principle possible, so long as the primordial magnetic field amplitude is small, but would require a very futuristic experiment with corresponding advances in calibration and foreground suppression techniques.

Item Type:Article
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URLURL TypeDescription Paper
Hirata, Christopher M.0000-0002-2951-4932
Additional Information:© 2018 American Physical Society. (Received 9 August 2017; published 21 May 2018) A. M. and C. H. are supported by the U.S. Department of Energy. C. H. is also supported by the David and Lucile Packard Foundation, the Simons Foundation, and NASA. We thank Olivier Doré, Michael Eastwood, Ashish Goel, and Tejaswi Venumadhav for useful discussions during the project.
Funding AgencyGrant Number
Department of Energy (DOE)UNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Simons FoundationUNSPECIFIED
Issue or Number:10
Record Number:CaltechAUTHORS:20180521-154938322
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86528
Deposited By: George Porter
Deposited On:21 May 2018 23:00
Last Modified:15 Nov 2021 20:39

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