1993 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/2786
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Item Nonlinear evolution of density perturbation(2015-01-17) Bagla, J. S.; Padmanabhan, T.From the epoch of recombination ( Z ≈103 ) till today, the typical density contrasts have grown by a factor of about 106 in Friedmann universe with Ω = 1. However, during the same epoch the typical gravitational potential has grown only by a factor of order unity. We present theoretical arguments explaining the origin of this approximate constancy of gravitational potential. This fact can be exploited to provide a new, powerful, approximation scheme to study the formation of nonlinear structures in the universe. The essential idea of this method is to evolve the initial distribution of particles using a gravitational potential frozen in time. We carry out this scheme for several standard models including the CDM and HDM and show that the results match quite well with those obtained by exact Numerical simulations. We compute different statistical measures of clustering and compare them for the description of nonlinear evolution. This approximation also provides valuable insight into understanding various features of nonlinear evolution; for example, it provides a simple explanation as to why pancakes remain thin during the evolution even in the absence of any artificial, adhesion-like, damping terms. We also compare this approximation with other schemes like Zeldovich approximation and frozen-flow. Our procedure has a far greater range of validity than the Zeldovic h approximation since it can handle motion across (and inside) caustic properly. Unlike in frozen-flow, actual shell-crossing does occur in the frozen-potential approximation; hence it provides a far more accurate description of the velocity field compared to frozen flow approximation.Item Nonlinear evolution of density perturbations using approximate constancy of gravitational potential(2015-01-13) Bagla, J. S.; Padmanabhan, T.