Nambu-Jona-Lasinio model in four dimensions at finite temperatures; chemical potential and curvature

The two-flavour Nambu-Jona-Lasinio model with N components is studied in cu rved spacetime at finite temperature and density in the leading 1/N expansi on. In four spacetime dimensions the model exhibits a first-order phase tra nsition for positive curvature. Whereas in flat space an increase in temper ature induces a second-order phase transition even at finite density, in cu rved space the transition becomes first order. We obtain the phase boundary in density-temperature plane and exhibit its behaviour with changing curva ture. A three-dimensional plot of the phase boundary in mu -T-R space is dr awn.