Distortion of secondaries in semi-detached binaries and the cataclysmic variable period minimum

Based on SPH simulations, we quantify the geometrical distortion eect due to tidal and rotational forces on polytropic secondaries in semi-detached binaries. The main eect is an expansion of the polytropic star, with an eect on the radius of5%{12%, depending on the polytropic index and the mass ratio. We apply such distortion eects to the secular evolution of secondaries in cataclysmic variable systems. We focus on systems below the 2{3 h period gap and that approach the minimum period. We nd a signicant increase of the predicted minimum period (4% if changes in the secondary's thermal relaxation are approximately taken into account). Though an improvement, the eect is not big enough to solve the mismatch between predicted and observed minimum period at 80 min.