Hybrid modified gravity unifying local tests, galactic dynamics and
  late-time cosmic acceleration
  The non-equivalence between the metric and Palatini formalisms of $f(R)$
gravity is an intriguing feature of these theories. However, in the recently
proposed hybrid metric-Palatini gravity, consisting of the superposition of the
metric Einstein-Hilbert Lagrangian with an $f(\cal R)$ term constructed \`{a}
la Palatini, the "true" gravitational field is described by the interpolation
of these two non-equivalent approaches. The theory predicts the existence of a
light long-range scalar field, which passes the local constraints and affects
the galactic and cosmological dynamics. Thus, the theory opens new
possibilities for a unified approach, in the same theoretical framework, to the
problems of dark energy and dark matter, without distinguishing a priori matter
and geometric sources, but taking their dynamics into account under the same
standard.
