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Effects of turbulent transfer on the critical behaviour

Critical behaviour of two systems, subjected to the turbulent mixing, is studied by means of the field theoretic renormalization group. The first system, described by the equilibrium model A, corresponds to relaxational dynamics of a non-conserved order parameter. The second one is the strongly nonequilibrium reaction-diffusion system, known as Gribov process or directed percolation process. The turbulent mixing is modelled by the stochastic Navier-Stokes equation with random stirring force with the correlator \propto δ(t-t') p^{4-d-y}, where p is the wave number, d is the space dimension and y the arbitrary exponent. It is shown that, depending on the relation between y and d, the systems exhibit various types of critical behaviour. In addition to known regimes (original systems without mixing and passively advected scalar field), existence of new strongly nonequilibrium universality classes is established, and the corresponding critical dimensions are calculated to the first order of the double expansion in y and ε=4-d (one-loop approximation).