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Review
, 4 (1), 1

The Cosmological Constant

Affiliations
Review

The Cosmological Constant

Sean M Carroll. Living Rev Relativ.

Abstract

This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero) vacuum energy.

Keywords: cosmological constant; cosmology; vacuum energy.

Figures

Figure 1
Figure 1
Dynamics for Ω = ΩM + ΩΛ. The arrows indicate the direction of evolution of the parameters in an expanding universe.
Figure 2
Figure 2
Expansion histories for different values of ΩM and ΩΛ. From top to bottom, the curves describe (ΩM, ΩΛ) = (0.3, 0.7), (0.3, 0.0), (1.0, 0.0), and (4.0, 0.0).
Figure 3
Figure 3
Hubble diagram (distance modulus vs. redshift) from the High-Z Supernova Team [214]. The lines represent predictions from the cosmological models with the specified parameters. The lower plot indicates the difference between observed distance modulus and that predicted in an open-universe model.
Figure 4
Figure 4
Hubble diagram from the Supernova Cosmology Project [197]. The bottom plot shows the number of standard deviations of each point from the best-fit curve.
Figure 5
Figure 5
Constraints in the ΩMΛ plane from the High-Z Supernova Team [214].
Figure 6
Figure 6
Constraints in the ΩMΛ plane from the Supernova Cosmology Project [197].
Figure 7
Figure 7
CMB data (binned) and two theoretical curves: The model with a peak at l ∼ 200 is a flat matter-dominated universe, while the one with a peak at l ∼ 400 is an open matter-dominated universe. From [35].
Figure 8
Figure 8
Constraints in the ΩMΛ plane from the North American flight of the BOOMERANG microwave background balloon experiment. From [171].
Figure 9
Figure 9
Gravitational lens probabilities in a flat universe with ΩM + ΩΛ = 1, relative to ΩM = 1, ΩΛ = 0, for a source at z = 2.
Figure 10
Figure 10
Limits from supernovae and large-scale structure data on ΩM and the equation-of-state parameter wX, in a flat universe dominated by matter and dark energy. Thin contours (on the left) represent limits from CMB and large-scale structure measurements, while thick contours are those from SNe observations; solid lines apply to models with constant wX, while dashed lines apply to models of dynamical scalar fields. The constraints are portrayed separately on the left, and combined on the right. From [194].
Figure 11
Figure 11
ΩΛ as a function of the scale factor a, for a universe in which ΩM0 = 0.3, ΩΛ0 = 0.7. Indicated are the scale factors corresponding to the Planck era, the electroweak phase transition, and Big Bang Nucleosynthesis.

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