Chiral symmetry in two-color QCD at finite temperature

We study chiral symmetry in two-color QCD with N-f massless flavors at finite temperature, using an effective theory. For the gauge group SU(2), the chiral symmetry group is enlarged to SU(2N(f)), which is then spontaneously broken to Sp(2N(f)) at zero temperature, At finite temperature, and when the axial anomaly can be neglected, we find a first order phase transition occurring for two or more flavors. In the presence of instantons, the symmetry restoration unambiguously remains first order for three pr more massless flavors. These results could be relevant for lattice studies of chiral symmetry at finite temperature and density.