Renormalization Group Equations in Critical Dynamics. I: Isotropic Heisenberg Ferromagnet

A renormalization group equation for the inverse propagator is obtained for a stochastic model of isotropic Heisenberg ferromagnet, whose solution at a fixed point yields the dynamical scaling law with the correct dynamic critical exponent. For 6-ε dimensions (ε>0) we describe an iterative method to obtain an ε-expansion for the inverse propagator.