Ohta-Jasnow-Kawasaki approximation for nonconserved coarsening under shear

We analytically study coarsening dynamics in a system with nonconserved sca lar order parameter, when a uniform time-independent shear flow is present. We use an anisotropic version of the Ohta-Jasnow-Kawasaki approximation to calculate the growth exponents in two and three dimensions: for d=3 the ex ponents we find are the same as expected on the basis of simple scaling arg uments, that is, 3/2 in the flow direction and 1/2 in all the other directi ons, while for d=2 we find an unusual behavior, in that the domains experie nce an unlimited narrowing for very large times and a nontrivial dynamical scaling appears. In addition, we consider the case where an oscillatory she ar is applied to a two-dimensional system, finding in this case a standard t(1/2) growth, modulated by periodic oscillations. We support our two-dimen sional results by means of numerical simulations and we propose to test our predictions by experiments on twisted nematic liquid crystals.