Squeezing the halo bispectrum: a test of bias models
  We study the halo-matter cross bispectrum in the presence of primordial
non-Gaussianity of the local type. We restrict ourselves to the squeezed limit,
for which the calculation are straightforward, and perform the measurements in
the initial conditions of N-body simulations, to mitigate the contamination
induced by nonlinear gravitational evolution. Interestingly, the halo-matter
cross bispectrum is not trivial even in this simple limit as it is strongly
sensitive to the scale-dependence of the quadratic and third-order halo bias.
Therefore, it can be used to test biasing prescriptions. We consider three
different prescription for halo clustering: excursion set peaks (ESP), local
bias and a model in which the halo bias parameters are explicitly derived from
a peak-background split. In all cases, the model parameters are fully
constrained with statistics other than the cross bispectrum. We measure the
cross bispectrum involving one halo fluctuation field and two mass overdensity
fields for various halo masses and collapse redshifts. We find that the ESP is
in reasonably good agreement with the numerical data, while the other
alternatives we consider fail in various cases. This suggests that the
scale-dependence of halo bias also is a crucial ingredient to the squeezed
limit of the halo bispectrum.
