UNIVERSALITY AND THE DECONFINEMENT PHASE-TRANSITION IN SU(2) LATTICE GAUGE-THEORY

We study the three-dimensional fundamental-adjoint SU(2) lattice gauge theory at non-zero temperatures by Monte Carlo simulations. On an 8(3 ) x 2 lattice, at beta(A) = 1.1, where beta(A) is the adjoint coupling , we find no evidence of any transition at the location of a previousl y known bulk phase transition around beta = 1.33. Moreover, the deconf inement transition at beta(A) = 1.1 occurs at beta = 1.20 and is of fi rst order for beta A greater than or equal to 1.1, thus implying a cha nge of universality class from that of the Wilson action at beta(A) = 0. Computations of the plaquette susceptibility and the temporal and s patial Polyakov loops on 8(3) x 4 and 16(3) x 8 lattices at beta(A) = 1.1 further support these conclusions and suggest that the previously claimed bulk transition around beta = 1.33 is, in fact, the first-orde r deconfinement transition. Simulations at larger beta(A) and the meas urements of the mass gaps from the correlation functions of temporal a nd spatial Polyakov loops also confirm the temperature dependent natur e of the above transition. The consequences of our results on universa lity are discussed.