ANALYSIS OF NONLINEAR MODE-COUPLING OF COSMOLOGICAL DENSITY-FLUCTUATIONS BY THE PSEUDOSPECTRAL METHOD

The pseudo-spectral method is proposed for following the evolution of density and velocity fluctuations at the weakly non-linear stage in th e expanding universe with good accuracy. With this method, the evoluti on of density and velocity fluctuations is integrated in the Fourier S pace using an FFT. This method is very useful to investigate accuratel y the non-linear dynamics in the weakly non-linear regime. Because the pseudo-spectral method works directly in the Fourier space, it should be especially useful for examining behavior in the Fourier domain, fo r example, the effects of the non-linear coupling of different wave mo des on the evolution of the power spectrum. The results of this analys is both in one- and three-dimensional systems are shown.