Optimized expansion in quantum field theory of massive fermions with (psi-barpsi)2 interaction

The optimized expansion for the generating functional for Green's functions in the path-integral representation is formulated in quantum field theory of fermions with a scalar Fermi interaction and compared with different expansion techniques. The effective action in n-dimensional space-time is calculated to the first order. Renormalization can be performed if the space-time dimension is less than four. In this case, the renormalized effective potential at a finite temperature is calculated to first order. The results suggest that the theory in two- and three-dimensional space-time is noninteracting or precarious