  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.
