Distinguishing cosmologies using the turn-around radius near galaxy
  clusters
  Outside galaxy clusters the competition between the inwards gravitational
attraction and the outwards expansion of the Universe leads to a special radius
of velocity cancellation, which is called the turn-around radius. Measurements
of the turn-around radius hold promises of constraining cosmological
parameters, and possibly even properties of gravity. Such a measurement is,
however, complicated by the fact that the surroundings of galaxy clusters are
not spherical, but instead are a complicated collection of filaments, sheets
and voids. In this paper we use the results of numerically simulated universes
to quantify realistic error-bars of the measurement of the turn-around radius.
We find that for a $\Lambda$CDM cosmology these error-bars are typically of the
order of $20\%$. We numerically simulate three different implementations of
dark energy models and of a scalar dark sector interaction to address whether
the turn-around radius can be used to constrain non-trivial cosmologies, and we
find that only rather extreme models can be distinguished from a $\Lambda$CDM
universe due to the large error-bars arising from the non-trivial cluster
environments.
