  The two loop effective potential of massless $\lambda\phi^4$ theory was
presented in several regularization and renormalization prescriptions and the
dynamical symmetry breaking solution was obtained in strong coupling situation
in several prescriptions except the Coleman-Weinberg prescription. The beta
function in the broken phase becomes negative and the UV fixed point turns out
to be a strong coupling one, and its numeric value varies with renormalization
prescriptions, a detail in difference from the asymptotic free solution in one
loop case. The symmetry breaking phase was shown to be an entirely strong
coupling phase. The reason of the relevance of the renormalization
prescriptions was shown to be due to the non-perturbative nature of the
effective potential. We also reanalyzed the two loop effective potential by
adopting a differential equation approach basing on the understanding that
takes all the QFT's as the ill-defined formulations of the 'low energy'
effective theories of a complete underlying theory. Then the relevance of the
prescriptions of fixing the local ambiguities to physical properties like
symmetry breaking was further emphasized. We also tentatively proposed a
rescaling insensitivity argument for fixing the quadratic ambiguities. Some
detailed properties of the strongly coupled broken phase and related issues
were discussed.
