Abstract:

The accelerating expansion of the universe is the most surprisingcosmological discovery in many decades, implying that the universe isdominated by some form of "dark energy" with exotic physical properties,or that Einstein's theory of gravity breaks down on cosmological scales.The profound implications of cosmic acceleration have inspired ambitiousexperimental efforts to measure the history of expansion and growth ofstructure with percent-level precision or higher. We review in detailthe four most well established methods for making such measurements:Type Ia supernovae, baryon acoustic oscillations (BAO), weakgravitational lensing, and galaxy clusters. We pay particular attentionto the systematic uncertainties in these techniques and to strategiesfor controlling them at the level needed to exploit "Stage IV" darkenergy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We brieflyreview a number of other approaches including redshift-spacedistortions, the Alcock-Paczynski test, and direct measurements of H_0.We present extensive forecasts for constraints on the dark energyequation of state and parameterized deviations from GR, achievable withStage III and Stage IV experimental programs that incorporatesupernovae, BAO, weak lensing, and CMB data. We also show the level ofprecision required for other methods to provide constraints competitivewith those of these fiducial programs. We emphasize the value of abalanced program that employs several of the most powerful methods incombination, both to cross-check systematic uncertainties and to takeadvantage of complementary information. Surveys to probe cosmicacceleration produce data sets with broad applications, and theycontinue the longstanding astronomical tradition of mapping the universein ever greater detail over ever larger scales.

Notes:

252 pages(!) 49 figures. Review article for Physics Reports. Comments welcome; those received before 2/17/12 will be considered before revised submission

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