Lee--Yang edge singularities in Nonlocal Nambu--Jona-Lasinio Model

Abstract

We investigate the QCD phase diagram and the associated Lee--Yang edge singularities using the two-flavor nonlocal Nambu--Jona-Lasinio model extended to complex chemical potential. There exists a strong correlation between the chiral phase transition and the structure of the effective potential in the complex order parameter plane, serving as a criterion to differentiate crossover from first-order transitions. Typically, the Lee--Yang edge singularities can be understood as a generalization of the critical end-point (CEP) between crossover and first-order transitions, where the positive Nambu phase and the Wigner phase coalesce. We further analyze the scaling behavior near the CEP by extracting the critical exponent associated with the Lee--Yang singularities. Additionally, we confirm that the extrapolation of the Lee--Yang edge singularity trajectories provides an effective method of determining the CEP location, even at a small real chemical potential. This provides a viable method for exploring regions of the QCD phase diagram that remain inaccessible to lattice QCD.