Parametrizing theories of gravity on large and small scales in cosmology
  We present a link between parametrizations of alternative theories of gravity
on large and small scales in cosmology. This relationship is established using
theoretical consistency conditions only. We find that in both limits the "slip"
and "effective Newton's constant" can be written in terms of a set of four
functions of time, two of which are direct generalizations of the $\alpha$ and
$\gamma$ parameters from post-Newtonian physics. This generalizes previous work
that has constructed frameworks for testing gravity on small scales, and is to
the best of our knowledge the first time that a link between parametrizations
of gravity on such very different scales has been established. We expect our
result to facilitate the imposition of observational constraints, by
drastically reducing the number of functional degrees of freedom required to
consistently test gravity on multiple scales in cosmology.
