Authors: Jack O. Burns (U. Colorado), S. Bale (UC-Berkeley), N. Bassett (U. Colorado), J. Bowman (ASU), R. Bradley (NRAO), A. Fialkov (U. Sussex), S. Furlanetto (UCLA), M. Hecht (Haystack Obs.), M. Klein-Wolt (Radbound U.), C. Lonsdale (Haystack Obs.), R. MacDowall (GSFC), J. Mirocha (McGill), J. Muñoz (Harvard), B. Nhan (U. Virginia), J. Pober (Brown), D. Rapetti (U. Colorado), A. Rogers (Haystack Obs.), K. Tauscher (U. Colorado)
Abstract: The Dark Ages, probed by the redshifted 21-cm signal, is the ideal epoch for a new rigorous test of the standard LCDM cosmological model. Divergences from that model would indicate new physics, such as dark matter decay (heating) or baryonic cooling beyond that expected from adiabatic expansion of the Universe. After the Cosmic Microwave Background photons decoupled from baryons, the Dark Ages epoch began: density fluctuations grew under the influence of gravity, eventually collapsing into the first stars and galaxies during the subsequent Cosmic Dawn. In the early Universe, most of the baryonic matter was in the form of neutral hydrogen (HI), detectable via its ground state’s “spin-flip” transition. A measurement of the redshifted 21-cm spectrum maps the history of the HI gas through the Dark Ages and Cosmic Dawn and up to the Epoch of Reionization (EoR), when ionization of HI extinguished the signal. The Experiment to Detect the Global EoR Signature (EDGES) recently reported an absorption trough at 78 MHz (redshift z~17), similar in frequency to expectations for Cosmic Dawn, but ~3 times deeper than was thought possible from standard cosmology and adiabatic cooling of HI. Interactions between baryons and slightly-charged dark matter particles with electron-like mass provide a potential explanation of this difference but other cooling mechanisms are also being investigated to explain these results.
Read via arXiv.