Density Perturbations in the Brans-Dicke Theory
  We analyse the fate of density perturbation in the Brans-Dicke Theory, giving a general classification of the solutions of the perturbed equations when the scale factor of the background evolves as a power law. We study with details the cases of vacuum, inflation, radiation and incoherent matter. We find, for the a negative Brans-Dicke parameter, a significant amplification of perturbations. 
J.P. Baptista, J.C. Fabris and S.V.B. Goncalves (Universidade Federal   do Espirito Santo - Brazil)