Angular momentum evolution can be predicted from cosmological initial
  conditions
  The angular momentum of dark matter haloes controls their spin magnitude and
orientation, which in turn influences the galaxies therein. However, the
process by which dark matter haloes acquire angular momentum is not fully
understood; in particular, it is unclear whether angular momentum growth is
stochastic. To address this question, we extend the genetic modification
technique to allow control over the angular momentum of any region in the
initial conditions. Using this technique to produce a sequence of modified
simulations, we can then investigate whether changes to the angular momentum of
a specified region in the evolved universe can be accurately predicted from
changes in the initial conditions alone. We find that the angular momentum in
regions with modified initial conditions can be predicted between 2 and 4 times
more accurately than expected from applying tidal torque theory. This result is
masked when analysing the angular momentum of haloes, because particles in the
outskirts of haloes dominate the angular momentum budget. We conclude that the
angular momentum of Lagrangian patches is highly predictable from the initial
conditions, with apparent chaotic behaviour being driven by stochastic changes
to the arbitrary boundary defining the halo.
