Quark number fluctuations in a chiral model at finite baryon chemical potential

We discuss the net quark and isovector fluctuations as well as off-diagonal quark flavor susceptibilities along the chiral phase transition line in the Nambu-Jona-Lasinio (NJL) model. The model is formulated at nonzero quark and isospin chemical potentials with nonvanishing vector couplings in the isoscalar and isovector channels. We study the influence of the quark chemical potential on the quark flavor susceptibilities in detail and the dependence of the results on model parameters as well as on the quark mass. The NJL model findings are compared with recent lattice results obtained in two-flavor QCD at finite chemical potential. On a qualitative level, the NJL model provides a consistent description of the dependence of quark number fluctuations on temperature and baryon chemical potential. The phase diagram and the position of the tricritical point in the NJL model are also discussed for different parameter sets.