Dark Energy after GW170817 and GRB170817A

The observation of GW170817 and its electromagnetic counterpart implies that gravitational waves travel at the speed of light, with deviations smaller than a few×10^{-15}. We discuss the consequences of this experimental result for models of dark energy and modified gravity characterized by a single scalar degree of freedom. To avoid tuning, the speed of gravitational waves must be unaffected not only for our particular cosmological solution but also for nearby solutions obtained by slightly changing the matter abundance. For this to happen, the coefficients of various operators must satisfy precise relations that we discuss both in the language of the effective field theory of dark energy and in the covariant…

• AN
  Agence Nationale de la Recherche

  Award: ANR-12-BS05-0002
• CN
  Centre National de la Recherche Scientifique
• IN
  Institut national des sciences de l'Univers