[astro-ph/0507263] Cosmic Growth History and Expansion History

Authors:  Eric V. Linder
Abstract:  The cosmic expansion history tests the dynamics of the global evolution of the universe and its energy density contents, while the cosmic growth history tests the evolution of the inhomogeneous part of the energy density. Precision comparison of the two histories can distinguish the nature of the physics responsible for the accelerating cosmic expansion: an additional smooth component - dark energy - or a modification of the gravitational field equations. With the aid of a new fitting formula for linear perturbation growth accurate to 0.2%, we separate out the growth dependence on the expansion history and introduce a new growth index parameter \gamma that quantifies the gravitational modification.
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gongbo zhao
Posts: 70
Joined: January 04 2005
Affiliation: ICG, Portsmouth

[astro-ph/0507263] Cosmic Growth History and Expansion Histo

Post by gongbo zhao » July 13 2005

I am puzzled about the formulation of part III.It seems there shouldn't be a "G" factor in the LHS of equations (8) -(11) compared with equation (1) of astro-ph/0304268 and equation (B7) of astro-ph/9804015 . Any comments on that ?

Ben Gold
Posts: 81
Joined: September 25 2004
Affiliation: University of Minnesota

[astro-ph/0507263] Cosmic Growth History and Expansion Histo

Post by Ben Gold » July 14 2005

I can only assume that by "G" in those equations he really means some dimensionless parameter like G(a)/G_N. That seems to be where's he's going with the next section. Otherwise the equations don't even pass a simple dimensional analysis test.

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