State of the Universe

Constraining the abundance of primordial black holes using EDGES 21-cm signal

by Mr. Shikhar Mittal (TIFR, Mumbai)

Friday, September 24, 2021 from to (Asia/Kolkata)
at Zoom link: (Meeting ID: 825 1295 6967 Passcode: 384194)
Using the global 21-cm signal measurement by the EDGES collaboration, we derive constraints on the fraction of the dark matter that is in the form of primordial black holes (PBHs) with masses in the range 10{15}-10{17} g. Improving upon previous analyses, we consider the effect of the X-ray heating of the intergalactic medium on these constraints and also use the full shape of the 21-cm absorption feature in our inference. In order to account for the anomalously deep absorption amplitude, we also consider an excess radio background motivated by LWA1 and ARCADE2 observations. Because the heating rate induced by PBH evaporation evolves slowly, the data favour a scenario in which PBH-induced heating is accompanied by X-ray heating. Also, for the same reason, using the full measurement across the EDGES observation band yields much stronger constraints on PBHs than just the redshift of absorption. We find that 21-cm observations exclude fPBH \grtsim 10{-9.7} at 95% CL for MPBH = 10{15} g. This limit weakens approximately as M_{\mathrm{PBH}}4 towards higher masses, thus providing the strongest constraints on ultralight evaporating PBHs as dark matter over the entire mass range 10{15}- 10{17} g.