Fluctuation Induced First Order Phase Transitions

We study a $U(N)\times U(N)$ symmetric scalar field model in four and three dimensions. First, using our data in four dimensions in the weak coupling region, we demonstrate explicitly that the observed first order phase transition is induced by quantum fluctuations. Next, based on the renormalization group and our new simulation results in three dimensions we argue that even if the $U_A(1)$ symmetry is restored below the critical temperature the QCD finite temperature chiral phase transition for two flavor could be extremely weak first order. Contribution to Lattice '93 proceedings. Needs espcrc2.sty file (included). Search Figure1.ps, Figure2.ps, … for postscript files.