Primordial Black-Hole Evaporation and the Quark-Gluon Phase Transition

The possibility that the Universe contains significant amounts of primordial black holes (PBHs) with a fraction of a solar mass (~ 10³² g or less) is not excluded at present. Although there are limits on the number of low-mass PBHs (m ~ 10¹⁵ g), there is some evidence for their existence. The abundance of PBHs is not inconsistent with the fluctuation density in the early Universe, especially near the time of the quark-gluon (Q-G) phase transition. We discuss a very interesting group of gamma-ray bursts (GRBs) of very short time duration and an increasing hard spectrum from the published BATSE catalog. We point out that the trend, i.e., anti-correlation of hardness ratio vs GRB duration, would be expected if some of the short GRBs came from black hole evaporation. We discuss the possibility that the onset of the Q-G plasma can give rise to such GRBs from PBH evaporation.