Abstract. We study effects of turbulent mixing on the random growth of an interface in the problem of the deposition of a substance on a substrate. The growth is modelled by the well-known Kardar-Parisi-Zhang model. The turbulent advecting velocity field is modelled by the Kraichnan's rapid-change ensemble: Gaussian statistics with the correlation function vv ∝ δ(t − twhere k is the wave number and 0 < ξ < 2 is a free parameter. Effects of compressibility of the fluid are studied. Using the field theoretic renormalization group we show that, depending on the relation between the exponent ξ and the spatial dimension d, the system reveals different types of largescale, long-time asymptotic behaviour, associated with four possible fixed points of the renormalization group equations. In addition to known regimes (ordinary diffusion, ordinary growth process, and passively advected scalar field), existence of a new nonequilibrium universality class is established. Practical calculations of the fixed point coordinates, their regions of stability and critical dimensions are calculated to the first order of the double expansion in ξ and ε = 2 − d (one-loop approximation). It turns out that for incompressible fluid, the most realistic values ξ = 4/3 or 2 and d = 1 or 2 correspond to the case of passive scalar field, when the nonlinearity of the KPZ model is irrelevant and the interface growth is completely determined by the turbulent transfer. If the compressibility becomes strong enough, the crossover in the critical behaviour occurs, and these values of d and ξ fall into the region of stability of the new regime, where the advection and the nonlinearity are both important. However, for this regime the coordinates of the fixed point lie in the unphysical region, so its physical interpretation remains an open problem.

Abstract. Standard field theoretic renormalization group is applied to the model of landscape erosion introduced by R. Pastor-Satorras and D. H. Rothman [Phys. Rev. Lett. 80: 4349 (1998); J. Stat. Phys. 93: 477 (1998)] yielding unexpected results: the model is multiplicatively renormalizable only if it involves infinitely many coupling constants, (i.e., the corresponding renormalization group equations involve infinitely many β-functions). Despite this fact, the one-loop counterterm can be derived albeit in a closed form in terms of the certain function V (h), entering the original stochastic equation, and its derivatives with respect to the height field h. Its Taylor expansion gives rise to the full infinite set of the one-loop renormalization constants, β-functions and anomalous dimensions. Instead of a set of fixed points, there is a two-dimensional surface of fixed points that is likely to contain infrared attractive region(s). If that is the case, the model exhibits scaling behaviour in the infrared range. The corresponding critical exponents are nonuniversal through the dependence on the coordinates of the fixed point on the surface, but satisfy certain universal exact relations.

Abstract. We study effects of the random fluid motion on a system in a self-organized critical state. The latter is described by the continuous stochastic model proposed by Hwa and Kardar [Phys. Rev. Lett. 62: 1813 (1989)]. The advecting velocity field is Gaussian, not correlated in time, with the pair correlation function of the form, where k ⊥ = |k ⊥ | and k ⊥ is the component of the wave vector, perpendicular to a certain preferred direction -the d-dimensional generalization of the ensemble introduced by Avellaneda and Majda [Commun. Math. Phys. 131: 381 (1990)]. Using the field theoretic renormalization group we show that, depending on the relation between the exponent ξ and the spatial dimension d, the system reveals different types of large-scale, long-time scaling behaviour, associated with the three possible fixed points of the renormalization group equations. They correspond to ordinary diffusion, to passively advected scalar field (the nonlinearity of the Hwa-Kardar model is irrelevant) and to the "pure" HwaKardar model (the advection is irrelevant). For the special case ξ = 2(4 − d)/3 both the nonlinearity and the advection are important. The corresponding critical exponents are found exactly for all these cases.

A new "static" renormalization group approach to stochastic models of fluctuating surfaces with spatially quenched noise is proposed in which only timeindependent quantities are involved. As examples, quenched versions of the Kardar-Parisi-Zhang model and its Pavlik's modification, the Hwa-Kardar model of selforganized criticality, and Pastor-Satorras-Rothman model of landscape erosion are studied. It is shown that the upper critical dimension in the quenched models is shifted by two units upwards in comparison to their counterparts with white in-time noise. Possible scaling regimes associated with fixed points of the renormalization group equations are found and the critical exponents are derived to the leading order of the corresponding ε expansions. Some exact values and relations for these exponents are obtained.

The effects of a randomly moving environment on a randomly growing interface are studied by the field theoretic renormalization group analysis. The kinetic growth of an interface (kinetic roughening) is described by the Kardar-Parisi-Zhang stochastic differential equation while the velocity field of the moving medium is modelled by the Navier-Stokes equation with an external random force. It is found that the large-scale, long-time (infrared) asymptotic behavior of the system is divided into four nonequilibrium universality classes related to the four types of the renormalization group equations fixed points. In addition to the previously established regimes of asymptotic behavior (ordinary diffusion, ordinary kinetic growth process, and passively advected scalar field), a new nontrivial regime is found. The fixed point coordinates, their regions of stability and the critical dimensions related to the critical exponents (e.g. roughness exponent) are calculated to the first order of the expansion in ε = 2 − d where d is a space dimension (one-loop approximation) or exactly. The new regime possesses a feature typical to the the Kardar-Parisi-Zhang model: the fixed point corresponding to the regime cannot be reached from a physical starting point. Thus, physical interpretation is elusive.