Browsing by Author "Kanekar, Nissim"

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Effects of anticorrelation on gravitational clustering
(Wiley-Blackwell, 2001-01-28) Kanekar, Nissim; Padmanabhan, T.
We use non-linear scaling relations (NSRs) to investigate the effects arising from the existence of negative correlations on the evolution of gravitational clustering in an expanding universe. It turns out that such anti-correlated regions have important dynamical effects on ıt all scales. In particular, the mere existence of negative values for the linear two-point correlation function ξbL over some range of scales starting from l = Lo, implies that the non-linear correlation function is bounded from above at ıt all scales x < Lo. This also results in the relation ξb ∝ x-3, at these scales, at late times, independent of the original form of the correlation function. Current observations do not rule out the existence of negative ξb for 200 h-1 Mpc ła ξb ła 1000 h-1 Mpc; the present work may thus have relevance for the real Universe. The only assumption made in the analysis is the ıt existence of the NSR; the results are independent of the form of the NSR as well as of the stable clustering hypothesis.
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.
Probing fundamental constant evolution with radio molecular spectroscopy
(2011-11-22) Kanekar, Nissim
Recycling the universe using scalar fields
(2001-07-02) Kanekar, Nissim; Sahni, Varun; Shtanov, Yuri
We examine the behaviour of a closed oscillating universe ﬁlled with a homogeneous scalar ﬁeld and ﬁnd that, contrary to naive expectations, such a universe expands to larger vol- umes during successive expansion epochs. This intriguing be- haviour introduces an arrow of time in a system which is time- reversible. The increase in the maximum size of the universe s closely related to the work done on/by the scalar ﬁeld dur- ng one complete oscillatory cycle which, in turn, is related to the asymmetry in the scalar ﬁeld equation of state dur- ng expansion and collapse. Our analysis shows that scalar ﬁelds with polynomial potentials V (φ) = λφq , q > 1 lead to a growing oscillation amplitude for the universe: the increase n amplitude between successive oscillations is more signiﬁ- cant for smaller values of q. Such behaviour allows for the eﬀective recycling of the universe. A recycled universe can be quite old and can resolve the ﬂatness problem. These results have strong bearing on cosmological models in which the role of dark matter is played by a scalar ﬁeld. They are also rele- vant for chaotic inﬂationary models of the early universe since they demonstrate that, even if the universe fails to inﬂate the ﬁrst time around, it will eventually do so during future oscil- atory cycles. Thus, the space of initial conditions favourable or chaotic inﬂation increases signiﬁcantly.