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Nonlinear Effects due to the Coupling of LongWave Modes  Bhuvnesh Jain
; Edmund Bertschinger
;  Date: 
27 Sep 1993  Abstract:  The cosmological fluid equations are used to study the nonlinear mode coupling of density fluctuations. We find that for realistic cosmological spectra there is a significant contribution to the nonlinear evolution on scales of interest to largescale structure from the longwave part of the initial spectrum. A consequence of this mode coupling is that at high redshift, $z$, the nonlinear scale [defined by $sigma(z)=1$] can be significantly larger than a linear extrapolation would indicate. For the standard CDM spectrum with a $sigma_8=1$ normalization the mass corresponding to the nonlinear scale at $z=20, 10, 5$ is about $100, 10, 3$ times (respectively) larger than the linearly extrapolated value. We also investigate the possibility of divergent contributions to the density field from longwave modes if the spectral index of the power spectrum $ n<1$. Using an approximate nonperturbative approach we find that for $n>3,$ the divergent contribution appears only in the phase. This can be related to the largescale bulk velocity, and clarifies previous results from Nbody simulations.  Source:  arXiv, astroph/9309040  Services:  Forum  Review  PDF  Favorites 


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