Long-wavelength Cosmological Perturbation in the Universe with Multiple   Perfect Fluids
  We investigate the large scale cosmological perturbation in the Universe with multiple perfect fluids. Using the long-wavelength approximation with Hamilton-Jacobi method, we derive the formula for the gauge invariant comoving curvature perturbation. As an application of our approach, we examine the large scale perturbation in a brane cosmology. 
Yasusada Nambu and Shin-ichi Ohokata