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We investigate gauge invariant cosmological perturbations in a spatially flatFriedman-Robertson-Walker universe with scalar fields. It is well known thatthe evolution equation for the gauge invariant quantities has exact solutionsin the long-wavelength limit. We find that these gauge invariant solutions canbe obtained by differentiating the background solution with respect toparameters contained in the background system. This method is very useful whenwe analyze the long-wavelength behavior of cosmological perturbation withmultiple scalar fields.Comment: 17 pages, will appear in Classical and Quantum Gravit

Solutions of gauge-invariant cosmological perturbations in the long-wavelength limit