Bispectrum Modelling in Large Scale Structure - A Three Shape Model
  We study the matter bispectrum of large structure by comparing theoretical
models (perturbation theories and halo models) to numerical simulations using
shape and amplitude correlators. We show that among the perturbation theories
at one loop the effective field theory of large scale structure extends the
furthest into the non-linear regime. We analyse the one and two-loop bispectra
in the renormalised perturbation theory and we show that there is a significant
extension in the range where results are accurate when going to two loops. In
the case of the halo model, we show that there are deficiencies in the
modelling of the two-halo term at redshifts z>0 that worsen in the past. Based
on this observation and on the shapes identified in the halo model, we build a
simple `three-shape model' that provides a good fit to N-body simulations on
all scales, at both low and high redshifts. We show that this model can be
easily extended to local and equilateral primordial non-Gaussianity using the
same shapes.
