  Nucleation is an out-of-equilibrium process, which can be strongly affected
by the presence of external fields. In this letter, we report a simple
extension of classical nucleation theory to systems submitted to an homogeneous
shear flow. The theory involves accounting for the anisotropy of the critical
nucleus formation, and introduces a shear rate dependent effective temperature.
This extended theory is used to analyze the results of extensive molecular
dynamics simulations, which explore a broad range of shear rates and
undercoolings. At fixed temperature, a maximum in the nucleation rate is
observed, when the relaxation time of the system is comparable to the inverse
shear rate. In contrast to previous studies, our approach does not require a
modification of the thermodynamic description, as the effect of shear is mainly
embodied into a modification of the kinetic prefactor and of the temperature.
