Testing spherical evolution for modelling void abundances
  We compare analytical predictions of void volume functions to those measured
from N-body simulations, detecting voids with the zobov void finder. We push to
very small, nonlinear voids, below few Mpc radius, by considering the unsampled
DM density field. We also study the case where voids are identified using
halos. We develop analytical formula for the void abundance of both the
excursion set approach and the peaks formalism. These formula are valid for
random walks smoothed with a top-hat filter in real space, with a large class
of realistic barrier models. We test the extent to which the spherical
evolution approximation, which forms the basis of the analytical predictions,
models the highly aspherical voids that occur in the cosmic web, and are found
by a watershed-based algorithm such as zobov. We show that the volume function
returned by zobov is quite sensitive to the choice of treatment of sub-voids, a
fact that has not been appreciated previously. For reasonable choices of
sub-void exclusion, we find that the Lagrangian density delta_v of the zobov
voids -- which is predicted to be a constant delta_v = -2.7 in the spherical
evolution model -- is different from the predicted value, showing substantial
scatter and scale dependence. This result applies to voids identified at z=0
with effective radius between 1 and 10 Mpc/h. Our analytical approximations are
flexible enough to give a good description of the resulting volume function;
however, this happens for choices of parameter values that are different from
those suggested by the spherical evolution assumption. We conclude that
analytical models for voids must move away from the spherical approximation in
order to be applied successfully to observations, and we discuss some possible
ways forward.
