Constraining PBH Mass Distributions from 21cm Brightness Temperature Results and an Analytical Mapping Between Probability Distribution of 21cm Signal and PBH Masses

The evaporation of Primordial Black Hole (PBH) via Hawking radiation influences the evolution of Inter Galactic Medium by heating up the latter and consequently affects the 21cm signal originated from the neutral Hydrogen atoms. In this work, we have considered EDGES observational data of 21cm line corresponding to cosmic dawn era to constrain the mass and the abundance of PBHs. In this context, two different PBH mass distributions namely, power law and lognormal mass distributions are considered to estimate the effects of PBH evaporation on the 21cm brightness temperature T_21. In addition to these two mass distributions, different monochromatic masses are also considered. The impacts of Dark Matter - baryon interactions on T_21 are also considered in this work along with the influences of PBH evaporation. Furthermore, adopting different monochromatic masses for PBHs, an attempt has been made to formulate a distribution for PBH masses by associating a probability weightage of the T_21 values (at z ∼ 17.2), within the range given by EDGES experiment, with the calculated T_21 values for each of the PBH mass values. The distribution best suited for the present purpose is found to be a combination of an error function and Owen function. Allowed contours in the parameter space of (initial PBH mass-dark matter mass) are obtained.