Dark Energy: constant or time variable? (… and other open questions)

Bharat Ratra (Kansas State University)

September 21, 2015

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Abstract: Experiments and observations over the last decade and a half have persuaded cosmologists that (as yet undetected) dark energy is by far the main component of the energy budget of the universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions.