The phase diagram of four flavor /SU(2) lattice gauge theory at nonzero chemical potential and temperature

SU(2) lattice gauge theory with four flavors of quarks is simulated at nonzero chemical potential μ and temperature T and the results are compared to the predictions of effective Lagrangians. Simulations on 16 ⁴ lattices indicate that at zero T the theory experiences a second order phase transition to a diquark condensate state. Several methods of analysis, including equation of state fits suggested by Chiral Perturbation Theory, suggest that mean-field scaling describes this critical point. Nonzero T and μ are studied on 12 ³×6 lattices. For low T, increasing μ takes the system through a line of second order phase transitions to a diquark condensed phase. Increasing T at high μ, the system passes through a line of first order transitions from the diquark phase to the quark-gluon plasma phase. Metastability is found near the first order line. Presumably, there is a tricritical point along this line of transitions. We estimate its position to be consistent with theoretical predictions.