Where the world stands still: turnaround as a strong test of \Lambda CDM
  cosmology
  Our intuitive understanding of cosmic structure formation works best in
scales small enough so that bound, relaxed gravitating systems are no longer
adjusting their radius; and large enough so that space and matter follow the
average expansion of the Universe. Yet one of the most robust predictions of
$\Lambda$CDM cosmology concerns the scale that separates these limits: the
turnaround radius, which is the non-expanding shell furthest away from the
center of a bound structure. The maximum possible value of the turnaround
radius within the framework of the $\Lambda$CDM model is, for a given mass $M$,
equal to $(3GM/\Lambda c^2)^{1/3}$, with $G$ Newton's constant and $c$ the
speed of light, independently of cosmic epoch, exact nature of dark matter, or
baryonic effects. We discuss the possible use of this prediction as an
observational test for $\Lambda$CDM cosmology.
