Global 21-cm brightness temperature in viscous dark energy models

Abstract

We investigate the observational excess of the EDGES experiment on the global 21-cm brightness temperature (−500 +200−500 mK at redshift 14 < z < 20) in the context of viscous dark energy (VDE) models. The bulk viscosity of dark energy perturbs the Hubble evolution of the Universe which could cool baryons faster, and hence, alter the 21-cm brightness temperature. An additional amount of entropy is also produced as an outcome of the viscous flow. We study the contribution of Hawking radiation from primordial black holes and baryon-dark matter scattering in the backdrop of VDE models towards modification of the 21-cm temperature. We obtain bounds on the VDE model parameters in order to account for the EDGES result due to the interplay of the above effects. Moreover, our analysis yields modified constraints on the dark matter mass and scattering crosssection compared to the case of the ΛCDM model.