  We extend a non local and non covariant version of the Thirring model in
order to describe a many-body system with spin-flipping interactions By
introducing a model with two fermion species we are able to avoid the use of
non abelian bosonization which is needed in a previous approach. We obtain a
bosonized expression for the partition function, describing the dynamics of the
collective modes of this system. By using the self-consistent harmonic
approximation we found a formula for the gap of the spin-charge excitations as
functional of arbitrary electron-electron potentials.
