COSMIC-RAYS FROM PRIMORDIAL BLACK-HOLES

We investigate the quantum emission from primordial black holes (PBHs) which may have formed from initial density perturbations or phase transitions in the early universe. In contrast to previous approaches, we assume that fundamental quarks, gluons, and leptons rather than the composite particles are directly emitted once the black hole thermal emission peaks above a few hundred MeV. The quark and gluon jets then fragment into the stable photons, leptons, and hadrons. We also consider how these particles are affected by interactions with the rest of the universe. If the PBHs formed from scale-invariant initial density perturbations in the radiation-dominated era, the emission can explain or contribute significantly to the extragalactic gamma-ray and interstellar cosmic-ray e-, e+, and pBAR backgrounds around 0.1-1 GeV. The PBH emission matches well the cosmic-ray gamma-ray spectrum between 50 and 170 MeV. The upper limits on the PBH density today from the gamma-ray, e+, e-, and pBAR data are comparable, provided that the PBHs cluster to the same degree as the other matter in the Galactic halo. The cosmic gamma-ray background places a constraint on the PBH density parameter of OMEGA-pbh less-than-or-similar-to 7.6(+/- 2.6) x 10(-9) h-1.95(+/- 0.15) for a universe with critical density, independent of clustering and Galactic interactions, corresponding to a limit on the initial density fluctuations of delta-rms less-than-or-similar-to 0.03 on scales below M congruent-to 5 x 10(14) g. Planck mass relics of the holes that have evaporated by today may contribute substantially to the dark matter. The emission is unlikely, though, to produce the 0.511 MeV annihilation line from the Galactic center. Gamma-ray bursts generated by the electron-positron emission in the ultimate stages of PBH evaporation are also practically undetectable. The direct explosive emission from an individual hole is not likely to be detected above the cosmic-ray backgrounds. In an alternative scenario, emission from PBHs with a less natural initial mass spectrum may explain the 0.6-10 MeV shoulder in the gamma-ray spectrum.