Effects of dark matter decay and annihilation on the high-redshift 21 cm background
- Yale Center for Astronomy and Astrophysics, Yale University, 260 Whitney Avenue, New Haven, Connecticut 06511 (United States)
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{approx}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(greater-or-similar sign)10{sup -24} eV cm{sup -3} sec{sup -1}. If all the dark matter is subject to decay, this allows us to constrain dark matter lifetimes(less-or-similar sign)10{sup 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{approx}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(less-or-similar sign)2 from the standard calculation at z{approx}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 H{sub 2} abundance, which may affect the earliest generations of stars and galaxies.
- OSTI ID:
- 20864089
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 74, Issue 10; Other Information: DOI: 10.1103/PhysRevD.74.103502; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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