Nonasymptotic critical dynamics near the superfluid transition in4He

Two-loop field theory and nonasymptotic properties of the dynamical model for the lambda transition in 3He-4He mixtures

Model F' introduced by Siggia and Nelson [Phys. Rev. B 15, 1427 (1977)] describes the critical dynamics of 3He-4He mixtures near the superfluid transition. Using the minimal subtraction scheme this model is renormalized within dynamical field theory. The dynamic zeta functions needed for the nonasymptotic flow properties are presented in two-loop order. The fixed points are discussed and the stable fixed points are identified. The transition to limiting models contained in model F' is shown analytically by performing the corresponding limits and numerically by calculating the nonlinear flow. These results are the basis for further experimental comparison of the transport coefficents in 3He-4He mixtures at higher concentrations including the tricritical point.