Dynamics of black holes in de Sitter spacetimes
  Nonlinear dynamics in cosmological backgrounds has the potential to teach us
immensely about our universe, and also to serve as prototype for nonlinear
processes in generic curved spacetimes. Here we report on dynamical evolutions
of black holes in asymptotically de Sitter spacetimes. We focus on the head-on
collision of equal mass binaries and for the first time compare analytical and
perturbative methods with full blown nonlinear simulations. Our results include
an accurate determination of the merger/scatter transition (consequence of an
expanding background) for small mass binaries and a test of the Cosmic
Censorship conjecture, for large mass binaries. We observe that, even starting
from small separations, black holes in large mass binaries eventually lose
causal contact, in agreement with the conjecture.
