q-Deformed grassmann fields and the two-dimensional Ising model

We construct an exact representation of the Ising partition function in the form of the SL_q(2, R)-invariant functional integral for the lattice-free q-fermion field theory (q=–1). It is shown that the q-fermionization allows one to rewrite the partition function of the eight-vertex model in an external field through a functional integral with four-fermion interaction. To construct these representations, we define a lattice (l, q, s)-deformed Grassmann bispinor field and extend the Berezin integration rules to this field. At q=–1, l=s=1, we obtain the lattice q-fermion field which allows us to fermionize the two-dimensional Ising model. We show that the Gaussian integral over (q, s)-Grassmann variables is expressed through the (q, s)-deformed Pfaffian which is equal to square root of the determinant of some matrix at q=±1, s=±1.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 103, No. 3, pp. 388–412. June, 1995.