Scalar density fluctuation at the critical end point in the Nambu–Jona-Lasinio model

The soft mode near the critical end point in the phase diagram of the two-flavor Nambu--Jona-Lasinio model is investigated within the leading 1/Nc approximation, with Nc being the number of colors. It is explicitly shown by studying the spectral function of the scalar channel that the relevant soft mode is the scalar density fluctuation, which is coupled with the quark number density, while the sigma meson mode stays massive.