Interaction corrections at intermediate temperatures: Magnetoresistance in a parallel field

We consider the correction to conductivity of a two-dimensional electron gas due to electron-electron interaction in the parallel magnetic field at arbitrary relation between temperature and the elastic mean free time. The correction exhibits nontrivial dependence on both temperature and the field. This dependence is determined by the Fermi-liquid constant, which accounts for the spin-exchange interaction. In particular, the sign of the slope of the temperature dependence is not universal and can change with the increase of the field.