2006/08/17 by Steven Furlanetto, Steven R. Furlanetto, S. Peng Oh +2
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #astro-ph
paper · pdf · doi:10.1103/physrevd.74.103502
published as Phys.Rev.D74:103502,2006 · submitted to Phys Rev D, 14 pages, 8 figures
arxiv created 2006/08/17 · openalex publication_date 2006/11/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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\ensuremath∼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\ensuremath\gtrsim10^\ensuremath-24 eV cm^\ensuremath-3 sec^\ensuremath-1. If all the dark matter is subject to decay, this allows us to constrain dark matter lifetimes\ensuremath\lesssim1027 sec. Such energy injection rates are much smaller than those typically probed by the CMB power spectra. The expected brightness temperature fluctuations at z\ensuremath∼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\ensuremath\lesssim2 from the standard calculation at z\ensuremath∼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.