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New probe of magnetic fields in the prereionization epoch. I. Formalism

Venumadhav, Tejaswi and Oklopčić, Antonija and Gluscevic, Vera and Mishra, Abhilash and Hirata, Christopher M. (2017) New probe of magnetic fields in the prereionization epoch. I. Formalism. Physical Review D, 95 (8). Art. No. 083010. ISSN 2470-0010.

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We propose a method of measuring extremely weak magnetic fields in the intergalactic medium prior to and during the epoch of cosmic reionization. The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition. This precession leads to a systematic change in the brightness temperature fluctuations of the 21-cm line from the high-redshift universe, and thus the statistics of these fluctuations encode information about the magnetic field the atoms are immersed in. The method is most suited to probing fields that are coherent on large scales; in this paper, we consider a homogenous magnetic field over the scale of the 21-cm fluctuations. Due to the long lifetime of the triplet state of the 21-cm transition, this technique is naturally sensitive to extremely weak field strengths, of order 10^(−19)  G at a reference redshift of ∼20 (or 10^(−21)  G if scaled to the present day). Therefore, this might open up the possibility of probing primordial magnetic fields just prior to reionization. If the magnetic fields are much stronger, it is still possible to use this method to infer their direction, and place a lower limit on their strength. In this paper (Paper I in a series on this effect), we perform detailed calculations of the microphysics behind this effect, and take into account all the processes that affect the hyperfine transition, including radiative decays, collisions, and optical pumping by Lyman-α photons. We conclude with an analytic formula for the brightness temperature of linear-regime fluctuations in the presence of a magnetic field, and discuss its limiting behavior for weak and strong fields.

Item Type:Article
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URLURL TypeDescription Paper
Venumadhav, Tejaswi0000-0002-1661-2138
Oklopčić, Antonija0000-0002-9584-6476
Hirata, Christopher M.0000-0002-2951-4932
Contact Email
Alternate Title:A new probe of magnetic fields in the pre-reionization epoch: I. Formalism
Additional Information:© 2017 American Physical Society. Received 4 December 2014; published 21 April 2017. We would like to thank Peter Goldreich and Takeshi Kobayashi for some helpful conversations during the early part of this work. T. V. acknowledges support from the Schmidt Fellowship and the Fund for Memberships in Natural Sciences at the Institute for Advanced Study. V. G. gratefully acknowledges the support of the Friends of the Institute for Advanced Study in Princeton. During the duration of this work, T. V. and A. O. were supported by the International Fulbright Science and Technology Award, and C. H., A. M., A. O., and T. V. were supported by the David and Lucile Packard Foundation, the Simons Foundation, and the U.S. Department of Energy. C. H. is also supported by NASA.
Funding AgencyGrant Number
Institute for Advanced StudyUNSPECIFIED
Fulbright FoundationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Simons FoundationUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Issue or Number:8
Classification Code:PACS numbers: 98.70.Vc, 98.62.Ra, 98.65.Dx
Record Number:CaltechAUTHORS:20141017-221623800
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50518
Deposited By: Tejaswi Nerella
Deposited On:21 Oct 2014 01:10
Last Modified:03 Oct 2019 07:24

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