Journal of Statistical Physics Vol. 49, Nos. 5/6, 1987. p. 1181-1190.
Using X-bounding (lower bounds by Laplacians with mixed boundary conditions and discrete analogs), we obtain the Lifschitz exponent at the bottom of the spectrum for random operators of type H_omega= T+V_omega, with T a (periodic) generator of a positivity-preserving semigroup, extending results by Kirsch and Simon.