  The self-consistent theory of localization is generalized to account for a
weak quadratic nonlinear potential in the wave equation. For spreading wave
packets, the theory predicts the destruction of Anderson localization by the
nonlinearity and its replacement by algebraic subdiffusion, while classical
diffusion remains unaffected. In 3D, this leads to the emergence of a
subdiffusion-diffusion transition in place of the Anderson transition. The
accuracy and the limitations of the theory are discussed.
