Localized rainbows in the QCD phase diagram
J. Maelger (Centre de Physique Théorique (CPHT), CNRS, Ecole Polytechnique, Institut Polytechnique de Paris, Route de Saclay, F-91128 Palaiseau, France, Astro-Particule et Cosmologie (APC), CNRS UMR 7164, Université Paris Diderot, 10, rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France); U. Reinosa (Centre de Physique Théorique (CPHT), CNRS, Ecole Polytechnique, Institut Polytechnique de Paris, Route de Saclay, F-91128 Palaiseau, France); J. Serreau (Astro-Particule et Cosmologie (APC), CNRS UMR 7164, Université Paris Diderot, 10, rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France)
We study the phase diagram of strongly interacting matter with light quarks using a recently proposed, small parameter approach to infrared QCD in the Landau gauge. This is based on an expansion with respect to both the inverse number of colors and the pure Yang-Mills coupling in the presence of a Curci-Ferrari mass term. At leading order, this leads to the well-known rainbow equation for the quark propagator with a massive gluon propagator and a tree-level quark-gluon vertex. We solve the latter at nonzero temperature and chemical potential using a simple semianalytic approximation known to capture the essence of chiral symmetry breaking in the vacuum. In the chiral limit, we find a tricritical point which becomes a critical end point in the presence of a nonzero bare quark mass, in agreement with the results of nonperturbative functional methods and model calculations.
