Dynamic roughening of directed lines

Abstract
We study the fluctuations of a stretched string, e.g., a vortex line, moving in a random medium. A pair of nonlinear equations are proposed to describe the evolution of longitudinal and transverse coordinates. The dynamic scaling of the fluctuations is studied analytically (by renormalization group) and numerically. In most cases the fluctuations are superdiffusive, governed by a dynamic exponent z=3/2.