Robust characteristics of non-Gaussian fluctuations from the NJL model

We evaluate the third- and fourth-order baryon, charge and strangeness susceptibilities near a chiral critical point using the Nambu-Jona-Lasinio model. We identify robust qualitative behaviors of the susceptibilities along hypothetical freeze-out lines that agree with previous model studies. Quantitatively, baryon number fluctuations are the largest in magnitude and thus offer the strongest signal when freeze-out occurs farther away from a critical point. Charge and strangeness susceptibilities also diverge at a critical point, but the area where the divergence dominates is smaller, meaning freeze-out must occur closer to a critical point for a signal to be visible in these observables. In the case of strangeness, this is attributable to the relatively large strange-quark mass. Plotting the third- and fourth-order susceptibilities against each other along the freeze-out line exhibits clearly their nonmontonicity and robust features.