Earth-mass primordial black hole mergers as sources for nonrepeating fast radio bursts

Fast radio bursts (FRBs) are mysterious astronomical radio transients with extremely short intrinsic duration. Until now, the physical origins of them still remain elusive, especially for the nonrepeating FRBs. Strongly inspired by recent progress on possible evidence of Earth-mass primordial black holes, we revisit the model of Earth-mass primordial black holes mergers as sources for nonrepeating FRBs. Under the null hypothesis that the observed nonrepeating FRBs originate from the mergers of Earth-mass primordial black holes, we analyzed four independent samples of nonrepeating FRBs to study the model parameters, i.e., the typical charge value q(c) and the power index alpha of the charge distribution function of the primordial black hole population phi(q) proportional to (q/q(c))(-alpha), which describe how the charge was distributed in the population. q is the charge of the hole in the unit of root GM, where M is the mass of the hole. It turns out that this model can explain the observed data well. Assuming the monochromatic mass spectrum for primordial black holes, we get the average value of typical charge (q) over bar (c)/10(-5) =1.59(-0.18)(+0.08) and the power index (alpha) over bar = 4.53(-0.14)(+0.21) by combining the fitting results given by four nonrepeating FRB samples. The event rate of the nonrepeating FRBs can be explained in the context of this model if the abundance of the primordial black hole populations with charge q greater than or similar to 10(-6) is larger than 10(-5), which is far below the upper limit given by current observations for the abundance of Earth-mass primordial black holes. In the future, simultaneous detection of FRBs and high frequency gravitational waves produced by mergers of Earth-mass primordial black holes may directly confirm or deny this model.