Variational Solution of the Gross-Neveu Model: finite N and Renormalization

We show how to perform systematically improvable variational calculations in the $O(2N)$ Gross-Neveu model for generic $N$, in such a way that all infinities usually plaguing such calculations are accounted for in a way compatible with the perturbative renormalization group . The final point is a general framework for the calculation of non-perturbative quantities like condensates, masses etc$\ldots$, in an asymptotically free field theory. For the Gross-Neveu model, the numerical results obtained from a ``2-loop'' down to low values of $N$.