The renormalization group flow properties in the neighborhood of the Gaussian fixed point

We consider four-component fermionic (Grassmann-valued) field on the hierarchical lattice. The Gaussian part of the Hamiltonian in the model is invariant under the block-spin renormalization group transformation with given degree of normalization factor (renormalization group parameter). The non-Gaussian part of the Hamiltonian is given by the sum of the self-interaction forms of the $2$-nd and $4$-th order. The action of the renormalization group transformation in this model is reduced to the rational map in the plane of coupling constants. We investigate the global dynamics of this map in the case when the coupling constant of the $4$-th order form is less than zero (lower half-plane) and the renormalization group parameter belongs to the interval $[1,3/2)$.