Dark Energy: The Observational Challenge

Abstract

Nearly all proposed tests for the nature of dark energy measure some combination of four fundamental observables: the Hubble parameter H(z), the distance-redshift relation d(z), the age-redshift relation t(z), or the linear growth factor D_1(z). I discuss the sensitivity of these observables to the value and redshift history of the equation of state parameter w, emphasizing where these different observables are and are not complementary. Demonstrating time-variability of w is difficult in most cases because dark energy is dynamically insignificant at high redshift. Time-variability in which dark energy tracks the matter density at high redshift and changes to a cosmological constant at low redshift is {\it relatively} easy to detect. However, even a sharp transition of this sort at z_c=1 produces only percent-level differences in d(z) or D_1(z) over the redshift range 0.4 < z < 1.8$, relative to the closest constant-w model. Estimates of D_1(z) or H(z) at higher redshift, potentially achievable with the Ly-alpha forest, galaxy redshift surveys, and the CMB power spectrum, can add substantial leverage on such models, given precise distance constraints at z < 2. The most promising routes to obtaining sub-percent precision on dark energy observables are space-based studies of Type Ia supernovae, which measure d(z) directly, and of weak gravitational lensing, which is sensitive to d(z), D_1(z), and H(z).

13 pages, to appear in proceedings of Wide Field Imaging From Space, New Astronomy Reviews, eds. T. McKay, A. Fruchter, and E. Linder

References in corpus (6)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Preliminary Maps and Basic Results
• Type Ia Supernova Discoveries at z>1 From the Hubble Space Telescope: Evidence for Past Deceleration and Constraints on Dark Energy Evolution
• Cosmological parameters from SDSS and WMAP
• Probing Dark Energy with Baryonic Acoustic Oscillations from Future Large Galaxy Redshift Surveys
• Probing dark energy using baryonic oscillations in the galaxy power spectrum as a cosmological ruler
• Dynamical Relaxation of the Cosmological Constant and Matter Creation in the Universe

Cited by in corpus (11)

• Observational Probes of Cosmic Acceleration
• Dark Energy
• Interacting Dark Energy and Dark Matter: observational Constraints from Cosmological Parameters
• Cylindrically Symmetric Solutions in $f(R,T)$ Gravity
• Bianchi Type $I$ Cosmology in $f(R,T)$ Gravity
• Gravitational Dust Collapse in $f(R)$ Gravity
• Uncertainty on determining the dark energy equation of state due to the spatial curvature
• The End of Cosmic Growth
• Exploring Plane Symmetric Solutions in $f(R)$ Gravity
• Observational constraints on the braneworld model with brane-bulk energy exchange
• Analytical considerations about the cosmological constant and dark energy