Nonlinear Dirac equations in D+1 space-time are obtained by variation of the
spinor action whose Lagrangian components have the same conformal degree and
the coupling parameter of the self-interaction term is dimensionless. In 1+1
dimension, we show that these requirements result in the "conventional" quartic
form of the nonlinear interaction and present the general equation for various
coupling modes. These include, but not limited to, the Thirring and Gross-Neveu
models. We obtain a numerical solution for the special case of the spin and
pseudo-spin symmetric modes..Comment: 8 pages, 2 figure
