Excluded volume, bag constant and hadron-quark phase transition

The model of hadron-quark phase transitions proposed by Cleymans et al. is modified by taking into account the fact that the nuclear repulsive force is operative between a pair of nucleons or a pair of antinucleons but not between a nucleon and an antinucleon. The phase boundary in the temperature (T)-chemical potential (μ) plane is calculated for some values of the bag constant B and the hard core radius R. Stability of the normal nuclear matter together with the bag picture for the nucleon yields rather stringent bounds for B as functions of R. The most probable range of values is estimated to be B1/4 ≅ 150 ≅ 200 MeV being consistent with the estimate from hadron spectroscopy. For this range of B, it is improbable to realize the broken chiral phase with deconfining constituent quarks and Goldstone pions at some T and μ. (orig.)