Lightening the Dark Matter from its Viscosity and Explanation of EDGES Anomaly

Understand

We study the visible photon production from the viscous dissipation of the dark matter (DM) fluid.

• The visible photon production depends on the magnitude of the dark matter viscosity and becomes important at the late times.
• We argue that for sufficiently large dark matter viscosity, the number of the resonantly converted visible photons becomes large which populates the Rayleigh-Jeans (RJ) tails of the Cosmic Microwave Background (CMB) radiation.
• Consequently, these excess visible photons possibly can explain the reported EDGES anomaly in the 21 cm signal.