Dark energy as an elastic strain fluid
  The origin of the accelerated expansion of the universe is still unclear and
new physics is needed on cosmological scales. We propose and test a novel
interpretation of dark energy as originated by an elastic strain due to a
cosmic defect in an otherwise Euclidean space-time. The strain modifies the
expansion history of the universe. This new effective contribution tracks
radiation at early times and mimics a cosmological constant at late times. The
theory is tested against observations, from nucleosynthesis to the cosmic
microwave background and formation and evolution of large scale structure to
supernovae. Data are very well reproduced with Lam\'e parameters of the order
of 10^{-52} m^{-2}.
