Research Papers (TP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/3

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Author: search.filters.author.Engineer, SunuSubject: search.filters.subject.Cosmology: Theory

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    Nonlinear gravitational clustering: Dreams of a paradigm
    (American Astronomical Society, 1997-09-08) Padmanabhan, T.; Engineer, Sunu
    We discuss the late-time evolution of the gravitational clustering in an expanding universe, based on the nonlinear scaling relations (NSR) that connect the nonlinear and linear two-point correlation functions. The existence of critical indices for the NSR suggests that the evolution may proceed toward a universal profle that does not change its shape at late times. We begin by clarifying the relation between the density profles of the individual halos and the slope of the correlation function, and we discuss the conditions under which the slopes of the correlation function at the extreme nonlinear end can be independent of the initial power spectrum. If the evolution should lead to a profle that preserves the shape at late times, then the correlation function should grow as a2 (in a )\1 universe), even at nonlinear scales. We prove that such exact solutions do not exist ; however, there exists a class of solutions ("psuedolinear profles") that evolve as a2 to a good approximation. It turns out that pseudolinear profles are the correlation functions that arise if the individual halos are assumed to be isothermal spheres. They are also confgurations of mass in which the nonlinear effects of gravitational clustering are a minimum, and hence they can act as building blocks of the nonlinear universe. We discuss the implications of this result.
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    Non-linear density evolution from an improved spherical collapse model
    (Wiley-Blackwell, 1999-11-30) Engineer, Sunu; Kanekar, Nissim; Padmanabhan, T.
    We investigate the evolution of non-linear density perturbations by taking into account the effects of deviations from spherical symmetry of a system. Starting from the standard spherical top hat model in which these effects are ignored, we introduce a physically motivated closure condition which specifies the dependence of the additional terms on the density contrast, δ. The modified equation can be used to model the behaviour of an overdense region over a sufficiently large range of δ. The key new idea is a Taylor series expansion in (1/δ) to model the non-linear epoch. We show that the modified equations quite generically lead to the formation of stable structures in which the gravitational collapse is halted at around the virial radius. The analysis also allows us to connect up the behaviour of individual overdense regions with the non-linear scaling relations satisfied by the two point correlation function. Comment: 11 pages, 6 figures. Final version, contains added discussion and modified figures to match the accepted version.