Landau Ginzberg model and deconfinement transition for extended SU(2) action

We compute the effective action in terms of the Polyakov loop for the 3-dimensional pure fundamental-adjoint SU(2) lattice gauge theory at non-zero temperatures using the strong coupling expansion. In the extended coupling plane we show the existence of a tricritical point where the nature of the deconfinement transition undergoes a change from second to first order. The resulting phase structure is in excellent agreement with the Monte Carlo results both in the fundamental and adjoint directions. The possible consequences of our results on universality are discussed.