Comments on Long-Wavelength Backreaction and Dark Energy
  In this brief note we comment on a recent attempt by Martineau and Brandenberger (astro-ph/0510523) to explain the acceleration of the Universe using the back-reaction of long-wavelength perturbations associated with isocurvature perturbation modes. 
E.W. Kolb (Fermilab and University of Chicago), S. Matarrese (Physics   Dept., University of Padova), A. Riotto (CERN, Geneva)