Energy injection in pre-recombination era and EDGES detection

Abstract

We study the possibility of explaining the recent EDGES detection by an energy injection in the pre-recombination era. Our aim is to show that the residue of this energy injection could give the resultant increase in the energy density at frequencies xe h =(kT) ' 10􀀀3, which is needed to explain the EDGES result. We consider two models of energy injection: Gaussian pro le with a xed redshift of injection and radiative decay of a nonrelativistic particle. We show that the energy injection should occur in the redshift range z . 4 103 to prevent free-free processes from thermalizing the injected energy. The injected energy should be nearly 200{1000 times the CMB intensity at xe ' 10􀀀3 to obtain the requisite residue. A large fraction of the injected energy gets thermalized and therefore distorts the CMB spectrum. We compute CMB spectral distortion for both the models and show that the fractional change in CMB energy density, CMB= CMB ' 10􀀀6, which might be detectable with the proposed experiment PIXIE. We also outline the implication of our proposed scenario for CMB anisotropies.