Constraints on a new post-general relativity cosmological parameter

Robert Caldwell, Asantha Cooray, and Alessandro Melchiorri
Phys. Rev. D 76, 023507 – Published 16 July 2007

Abstract

A new cosmological variable is introduced to characterize the degree of departure from Einstein’s general relativity with a cosmological constant. The new parameter, ϖ, is the cosmological analog of γ, the parametrized post-Newtonian variable which measures the amount of spacetime curvature per unit mass. In the cosmological context, ϖ measures the difference between the Newtonian and longitudinal potentials in response to the same matter sources, as occurs in certain scalar-tensor theories of gravity. Equivalently, ϖ measures the scalar shear fluctuation in a dark-energy component. In the context of a vanilla, cosmological constant-dominated universe, a nonzero ϖ signals a departure from general relativity or a fluctuating cosmological constant. Using a phenomenological model for the time evolution ϖ=ϖ0ρDE/ρM which depends on the ratio of energy density in the cosmological constant to the matter density at each epoch, it is shown that the observed cosmic microwave background temperature anisotropies limit the overall normalization constant to be 0.4<ϖ0<0.1 at the 95% confidence level. Existing measurements of the cross-correlations of the cosmic microwave background with large-scale structure further limit ϖ0>0.2 at the 95% CL. In the future, integrated Sachs-Wolfe and weak lensing measurements can more tightly constrain ϖ0, providing a valuable clue to the nature of dark energy and the validity of general relativity.

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  • Received 10 March 2007

DOI:https://doi.org/10.1103/PhysRevD.76.023507

©2007 American Physical Society

Authors & Affiliations

Robert Caldwell

  • Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, New Hampshire 03755 USA

Asantha Cooray

  • Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, California 92697 USA

Alessandro Melchiorri

  • Physics Department and Sezione INFN, University of Rome “La Sapienza,” P.le Aldo Moro 2, 00185 Rome, Italy

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Vol. 76, Iss. 2 — 15 July 2007

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