The cosmological constant is back

  title={The cosmological constant is back},
  author={Lawrence Krauss and Michael S. Turner},
  journal={General Relativity and Gravitation},
A diverse set of observations now compellingly suggest that the universe possesses a nonzero cosmological constant. In the context of quantum-field theory a cosmological constant corresponds to the energy density of the vacuum, and the favored value for the cosmological constant corresponds to a very tiny vacuum energy density. We discuss future observational tests for a cosmological constant as well as the fundamental theoretical challenges — and opportunities — that this poses for particle… 

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