Application of the Renormalization Group to a Second-Order QCD Phase Transition

An earlier suggestion that the chiral phase transition in QCD for two flavors of massless quarks might be a second-order transition has gained credibility as a result of recent numerical simulations. One can test this hypothesis, and draw very specific quantitative consequences from it, using universality and renormalization group ideas. This hypothetical second order phase transition is in the universality class of a four component isotropic Heisenberg antiferromagnet—a model which has been investigated intensely by condensed matter physicists. Existing calculations can be adapted to yield predictions for critical exponents governing the QCD transition. The perturbation due to small equal quark masses maps onto an external staggered magnetic field; that due to unequal quark masses is effective only in second order and generates a quadratic anisotropy. Several other potential applications of the renormalization group to related questions are suggested, including a model of the tricritical point which arises with finite strange quark mass, and a model for the dynamic critical behavior.