Nature of the NJL critical end point

The behavior of the scalar channel spectral function is investigated near the critical end point on the temperature-quark chemical potential plane of two-flavor Nambu-Jona-Lasinio (NJL) model within the leading 1/Nc approximation with Nc being the number of colors. It is found that the relevant soft mode at the critical end point is the scalar density fluctuation with space-like dispersion, which is mixed with those of the quark-number and entropy densities, while on the other hand the sigma meson mode stays massive. (Slightly condensed version of the paper, hep-ph/0302167). (author)