Random interface growth in a random environment: Renormalization group analysis of a simple model

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 $\langle vv\rangle \propto \delta(t-t') \, k^{-d-\xi}$, where $k$ is the wave number and $0<\xi<2$ 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 $\xi$ and the spatial dimension $d$, the system reveals different types of large-scale, 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 $\xi$ and $\varepsilon=2-d$ (one-loop approximation). It turns out that for incompressible fluid, the most realistic values $\xi=4/3$ 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 $\xi$ fall into the region of stability of the new regime, where the advection and the nonlinearity are both important.