Heat transfer between baryons and millicharged dark matter has been invoked as a possible explanation for the anomalous 21-cm absorption signal seen by EDGES. Prior work has shown that the solution requires that millicharged particles make up only a fraction (mχ/MeV) 0.0115% f 0.4% of the dark matter and that their mass mχ and charge qχ have values 0.1 (mχ/MeV) 10 and 10 −6 (qχ/e) 10 −4 . Here we show that such particles come into chemical equilibrium before recombination, and so are subject to a constraint on the effective number N eff of relativistic degrees of freedom, which we update using Planck 2018 data. We moreover determine the precise relic abundance f that results for a given mass mχ and charge qχ and incorporate this abundance into the constraints on the millicharged-dark-matter solution to EDGES. With these two results, the solution is ruled out if the relic abundance is set by freeze-out.

Compact dark matter has been efficiently constrained in the M 10 M mass range by null searches for microlensing of stars in nearby galaxies. Here we propose to probe the mass range M 10 M by seeking echoes in gamma-ray-burst light curves induced by strong lensing. We show that strong gravitational lensing of gamma ray bursts (GRBs) by massive compact halo objects (MACHOs) generates superimposed GRB images with a characteristic time delay of 1 ms for M 10 M . Using dedicated simulations to capture the relevant phenomenology of the GRB prompt emission, we calculate the signal-to-noise ratio required to detect GRB lensing events as a function of the flux ratio and time delay between the lensed images. We then analyze existing data from the Fermi/GBM and Swift/BAT instruments to assess their constraining power on the compact dark matter fraction fDM. We find that this data is noise limited, and therefore localization-based masking of background photons is a key ingredient. Future observatories with better sensitivity will be able to probe down to the fDM 1% level across the 10 M M 1000 M mass range.arXiv:1809.09627v2 [astro-ph.CO]

No abstract

No abstract

No abstract