The phase transition from nuclear matter to quark matter during proto-neutron star evolution

We explore the occurrence of a phase transition from nuclear matter to quark matter in proto-neutron stars. To this end, we employ recent results on such a phase transition in the presence of an electron-neutrino-degenerate gas, based on a mean field model nuclear equation of state together with a quark matter equation of state as described by the MIT 'bag model'. Those results show that this neutrino gas does not favour the transition. By comparison with the proto-neutron star evolutionary calculations of Keil & Janka, we find that, if the bag constant B has a value B less than or similar to 126 MeV fm(-3), the deconfinement transition indeed occurs. We also find that, if B greater than or similar to 100 MeV fm(-3), the phase transition is delayed by the presence of neutrinos by a few seconds after core bounce, thus providing a natural explanation for the second peak of neutrino emission detected in SN 1987A by the Kamiokande Group. The transition to quark matter and its subsequent decay should affect proto-neutron star evolution and supernova explosions in a non-trivial way.