On a mean field approximation for Higgs-Yukawa systems

Abstract

We discuss the phase structure of a lattice Higgs-Yukawa system in the variational mean field approximation with contributions of fermionic determinant being calculated in a ladder approximation. In particular, we demonstrate that in this approximation the ferrimagnetic phase in the $Z_2$ model with naive fermions can appear as an artifact of a finite lattice and that the phase diagram for this model on infinite lattice changes qualitatively at space-time dimension $D=4$ compared with those at $D>4$.

Comments: 11 pages, 5 PostScript figures ( included ), harvmac and epsf, KYUSHU-HET-7. ( All is the same as the original one except that the EPSF macro is used for figures. Some PostScript errors in figures are removed.)