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[23.02] Methods of Constraining the Equation of State: An Overview

D. H. Weinberg (Ohio State University)

I will review proposed methods for constraining the equation of state of dark energy. These methods test models of the cosmic expansion history by measuring either the distance-redshift relation d(z), the Hubble parameter H(z), the age of the universe t(z), the linear growth factor D₁(z), or some combination of these quantities. Observational probes include supernovae, clusters of galaxies, galaxy counts, galaxy ages, strong and weak gravitational lensing, properties of the Lyman-alpha forest, and CMB anisotropies. Different measurements can provide complementary constraints on Omega_vac, the vacuum energy density parameter, and w_eff, the effective equation of state parameter. If w_eff is substantially different from -1 (the value for a pure cosmological constant), then this departure should be detected independently by several methods within a few years. Distinguishing a model with time-dependent w from a model with constant w is much more difficult, typically requiring sub-percent measurement precision. It is not clear that any method can control systematic errors well enough to achieve this precision, though supernovae look like they have the best chance to do so.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.