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Effects of dark matter decay and annihilation on the high-redshift 21 cm background

Furlanetto, Steven R. and Oh, S. Peng and Pierpaoli, Elena (2006) Effects of dark matter decay and annihilation on the high-redshift 21 cm background. Physical Review D, 74 (10). Art. No. 103502. ISSN 2470-0010. doi:10.1103/PhysRevD.74.103502.

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The radiation background produced by the 21 cm spin-flip transition of neutral hydrogen at high redshifts can be a pristine probe of fundamental physics and cosmology. At z~30–300, the intergalactic medium (IGM) is visible in 21 cm absorption against the cosmic microwave background (CMB), with a strength that depends on the thermal (and ionization) history of the IGM. Here we examine the constraints this background can place on dark matter decay and annihilation, which could heat and ionize the IGM through the production of high-energy particles. Using a simple model for dark matter decay, we show that, if the decay energy is immediately injected into the IGM, the 21 cm background can detect energy injection rates>~10^-24 eV cm^-3 sec^-1. If all the dark matter is subject to decay, this allows us to constrain dark matter lifetimes<~10^27 sec. Such energy injection rates are much smaller than those typically probed by the CMB power spectra. The expected brightness temperature fluctuations at z~50 are a fraction of a mK and can vary from the standard calculation by up to an order of magnitude, although the difference can be significantly smaller if some of the decay products free stream to lower redshifts. For self-annihilating dark matter, the fluctuation amplitude can differ by a factor<~2 from the standard calculation at z~50. Note also that, in contrast to the CMB, the 21 cm probe is sensitive to both the ionization fraction and the IGM temperature, in principle allowing better constraints on the decay process and heating history. We also show that strong IGM heating and ionization can lead to an enhanced H2 abundance, which may affect the earliest generations of stars and galaxies.

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Furlanetto, Steven R.0000-0002-0658-1243
Pierpaoli, Elena0000-0002-7957-8993
Additional Information:© 2006 The American Physical Society. (Received 10 August 2006; published 1 November 2006) S.R.F. thanks the Tapir group at Caltech for their hospitality while much of this work was completed and M. McQuinn for helpful discussions. E.P. is supported by NSF Grant No. AST-0340648 and is also supported by NASA Grant No. NAG5-11489. S.P.O. gratefully acknowledges NSF Grant No. AST-0407084 and NASA Grant No. NNG06GH95G for support.
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Issue or Number:10
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6387
Deposited By: Archive Administrator
Deposited On:06 Dec 2006
Last Modified:08 Nov 2021 20:33

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