2011 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/151
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Item Statefinder hierarchy: An extended null diagnostic for concordance cosmology(2011-01-04) Arabsalmani, Maryam; Sahni, VarunWe 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.Item Generalizing the cosmic energy equation(2011-01-01) Shtanov, Yuri; Sahni, VarunWe generalize the cosmic energy equation to the case when massive particles in- teract via a modified gravitational potential of the form .(a, r), which is allowed to explicitly depend on the cosmological time through the expansion factor a(t). Using the nonrelativistic approximation for particle dynamics, we derive the equation for the cosmological expansion which has the form of the Friedmann equation with a renormalized gravitational constant. The generalized Layzer–Irvine cosmic energy equation and the associated cosmic virial theorem are applied to some recently pro- posed modifications of the Newtonian gravitational interaction between dark-matter particles. We also draw attention to the possibility that the cosmic energy equation may be used to probe the expansion history of the universe thereby throwing light on the nature of dark matter and dark energy.