Melting the Diquark Condensate in Two-Color QCD: A Renormalization Group Analysis

We use a Landau theory and the epsilon expansion to study the superfluid phase transition of two-color QCD at nonzero temperature, T, and baryonic chemical potential, mu. At low T, and for N_f flavors of massless quarks, the global SU(N_f) \times SU(N_f) \times U(1) symmetry is spontaneously broken by a diquark condensate down to Sp(N_f) \times Sp(N_f) for any mu > 0. As the temperature increases, the diquark condensate melts, and at sufficiently large T the symmetry is restored. Using renormalization group arguments, we find that in the presence of the chiral anomaly term there can be a second order phase transition when N_f=2 or N_f >= 6, while the transition is first order for N_f=4. We discuss the relevance of these results for the emergence of a tricritical point recently observed in lattice simulations.