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The EDGES experiment has detected with high S/N an absorption feature in the radio spectrum centered at 78 MHz. This feature is broadly consistent with expectations for the global 21-cm absorption signal from cosmic dawn. However, important aspects of the signal differ from physical predictions. In particular, 1) its absorption amplitude is larger than expected, 2) its profile has surprisingly sharp features, and 3) the center frequency is in tension with predictions from high-z UV galaxy luminosity functions. Understanding the key experimental aspects is crucial when interpreting this challenging measurement. In my talk I will describe the EDGES detection of this absorption feature using our two Low-Band instruments. I will discuss the lab and field calibrations, the verifications tests, the data analysis, and the parameter estimation. I will also summarize recent efforts to constrain traditional 21-cm models using EDGES High-Band data.
Dark matter revealed by the first stars?45m4-3-006 - TH Conference Room
The EDGES global 21-cm experiment has detected stronger absorption than expected at cosmic dawn. This absorption can be explained by invoking excess cooling of the cosmic gas induced by an interaction with dark matter. This would have far reaching consequences, including an upper limit on the mass of dark matter particles that conflicts with the expectations for WIMPs. Specific particle physics models are highly constrained, but further observations will decide. In particular, we predict that 21-cm fluctuations at cosmic dawn are likely to be much larger than previously expected, and may exhibit a specific signature of the effect of dark matter.
Possible attempts to resolve the EDGES anomaly rely on cooling cosmic hydrogen gas via interactions between dark and visible sector or modifying the soft photon background beyond CMB. The first solution is in tension with cosmological dark matter probes once simple dark sector models are considered. The second solution can be realised as soft photon emission from dark sector. However, the proposed mechanisms to produce soft photons need rather complex physics, e.g. axion miniclusters. The talk is based on our recent paper 1803.03245.
Constraints on energy injection from 21-cm measurements: primordial black holes, axion-like particles and excited dark matter30m4-3-006 - TH Conference Room
The global 21-cm absorption signal induced by the first stars provides unique insights into structure formation at very high redshifts. I will show how the timing of such a signal can be used to obtain unprecedented constraints on the nature of dark matter.
The observation of an absorption feature in the 21 cm spectrum at redshift z ≈ 17 implies bounds on Dark Matter annihilations for a broad range of masses, given that significant heating of the intergalactic medium would have erased such feature. The resulting bounds on the DM annihilation cross sections are comparable to the strongest ones from all other observables.
Stronger 21cm absorption from charge sequestration30m4-3-006 - TH Conference Room
The unexpectedly strong 21cm absorption signal detected by the EDGES experiment suggests that the baryonic gas at the end of the dark ages was colder than predicted in the standard scenario. We discuss a mechanism to lower the baryon temperature after recombination. We introduce a stable, negatively-charged particle with a significant cosmological abundance, such that the universe remains charge-neutral but the electron and proton numbers are no longer equal. The deficit of electrons after recombination results in an earlier decoupling of the baryon and CMB temperatures, and thus in a colder gas at the cosmic dawn.