Meson properties and chiral transition at finite temperature and density in Nambu-Jona-Lasinio model with different regularization schemes

Modifications of meson and baryon properties due to the presence of an external hot baryon medium are investigated in the Nambu-Jona-Lasinio model. The corresponding meson sector is solved for a quark continuum at finite density and temperature. We use two regularization schemes with 3-dimensional sharp, Pauli-Villars and proper time cut-off types. Due to the medium the constituent quark mass and the pion and sigma masses are modified. We find a first-order chiral phase transition at relatively low temperatures less than 100 MeV which changes to second order at higher temperatures. The corresponding temperature-density phase diagram is non-monotonic. 5 figs., 1 tab., 33 refs. (author)