Abstract

The Bethe strip of width m is the Cartesian product B x {1,..., m}, where B is the Bethe lattice (Cayley tree). We consider Anderson-like Hamiltonians H-lambda = 1/2 Delta circle times 1 + 1 circle times A + lambda V on a Bethe strip with connectivity K >= 2, where A is an m x m symmetric matrix, V is a random matrix potential, and lambda is the disorder parameter. Under certain conditions on A and K, for which we previously proved the existence of absolutely continuous spectrum for small lambda, we now obtain ballistic behavior for the spreading of wave packets evolving under H-lambda for small lambda.