2011 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/151

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Subject: search.filters.subject.Cosmology

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    Statefinder hierarchy: An extended null diagnostic for concordance cosmology
    (2011-01-04) Arabsalmani, Maryam; Sahni, Varun
    We show how higher derivatives of the expansion factor can be developed into a null diagnostic for concordance cosmology (ΛCDM). It is well known that the Statefinder – the third derivative of the expansion factor written in dimensionless form, a (ᶟ) /aH ᶟ , equals unity for ΛCDM. We generalize this result and demonstrate that the hierarchy, a (ᴺ) /aH ᴺ , can be converted to a form that stays pegged at unity in concordance cosmology. This remarkable property of the Statefinder hierarchy enables it to be used as an extended null diagnostic for the cosmological constant. The Statefinder hierarchy, combined with the growth rate of matter perturbations, can serve as a composite null diagnostic to differentiate between dark energy models.
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    Entropy changes in the clustering of galaxies in an expanding universe
    (2011-05-26) Iqbal, Naseer; Khan, Mohammad Shafi; Masood, Tabasum
    In the present work the approach-thermody-namics and statistical mechanics of gravitating systems is applied to study the entropy changein gravitational clustering of galaxies in an ex-panding universe. We derive analytically the expressions for gravitational entropy in terms of temperature T and average density n of the par-ticles (galaxies) in the given phase space cell. It is found that during the initial stage of cluster-ing of galaxies, the entropy decreases and finally seems to be increasing when the system attains virial equilibrium. The entropy changes are studied for different range of measuring correlation parameter b. We attempt to provide a clearer account of this phenomena. The entropy esults for a system consisting of extended mass (non-point mass) particles show a imilar behaviour with that of point mass particles clustering gravitationally in an expanding uni-verse.
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    Beyond the standard cosmological model with CMB
    (2011-06-02) Souradeep, Tarun
    Measurements of CMB anisotropy and, more recently, polarization have played a very important role in cosmology. Besides precise determination of various parameters of the ‘standard’ cosmological model, observations have also established some important basic tenets that underlie models of cosmology and structure formation in the universe – ‘acausally’ correlated, adiabatic, primordial perturbations in a flat, statistically isotropic universe. These are consistent with the expectation of the paradigm of inflation and the generic prediction of the simplest realization of inflationary scenario in the early universe. Further, gravitational instability is the established mechanism for structure formation from these initial perturbations. Primordial perturbations observed as the CMB anisotropy and polarization is the most compelling evidence for new, possibly fundamental, physics in the early universe. The community is now looking beyond the parameter estimation of the ‘standard’ model, for subtle, characteristic signatures of early universe physics.