511 keV galactic line from first-order phase transitions and primordial black holes

Abstract

Hawking evaporation of primordial black hole (PBH), with mass $3\times 10^{-17}\lesssim M_{\mathrm{PBH}}/M_{\odot }\lesssim 7\times 10^{-17}$ and fractional abundance $0.01\lesssim f_{\mathrm{PBH}}\lesssim 0.5$, well reproduces 511 keV gamma-ray excess from galaxy center. In this work, we investigated the production mechanism of PBHs base on the first-order phase transition induced by quartic effective thermal potential of a scalar field in dark sector. We found the phase transition with vacuum energy, $\mathcal{O}(1)\lesssim B^{1/4}/\mathrm{MeV}\lesssim \mathcal{O}(100)$, produces the desired PBH mass and abundance fraction. Correlated signatures of gravitational wave and extragalactic gamma-ray from phase transition and black hole evaporation, respectively, are within $\mu$Ares and AMEGO/e-ASTROGAM projected sensitivities.