One of the distinctive features of the QCD phase diagram is the possible emergence of a critical endpoint. The critical region around the critical point and the path dependency of the critical exponents are investigated within effective chiral ($2+1$)-flavor models with and without Polyakov loops. Results obtained in no-sea mean-field approximations where a divergent vacuum part in the fermion-loop contribution is neglected are compared to the renormalized ones. Furthermore, the modifications caused by the backreaction of the matter fluctuations on the pure Yang-Mills system are discussed. Higher-order, non-Gaussian moments of event-by-event distributions of various particle multiplicities are enhanced near the critical point and could serve as a probe to determine its location in the phase diagram. By means of a novel derivative technique higher-order generalized quark-number susceptibilities are calculated and their sign structure in the phase diagram is analyzed.

• Received 7 December 2011

DOI:https://doi.org/10.1103/PhysRevD.85.034027