Z(2)-symmetry restoration in the lambda phi(4) field theory with normal-ordering renormalization

Using the Gaussian wavefunctional approach plus normal-ordering renormaliza tion, Ne show that for the lambda phi(4) field theory, the discrete Z(2)-sy mmetry broken at the classical level is restored within some parameter regi on not only in (1+1) dimensions but also in (2+1) and (3+1) dimensions.