Precise Calibration of the One-Loop Bispectrum in the Effective Field
  Theory of Large Scale Structure
  The bispectrum is the leading non-Gaussian statistic in Large-Scale Structure
(LSS) clustering and encodes the interactions in the underlying field. It is
thus an important diagnostic for primordial non-Gaussianity and higher order
galaxy biasing. In this paper we present a detailed test and calibration of the
matter bispectrum counterterms in the Effective Field Theory of LSS against a
suite of $N$-body simulations. We are going beyond previous studies in
employing realisation based perturbation theory that allows for a significant
reduction in cosmic variance error bars. This enables the measurement of the
low-energy constants on large scales before two-loop corrections become
relevant, around $k<0.09 h\mathrm{Mpc}^{-1}$ at $z=0$. We also go beyond
previous work in using bispectrum propagator terms, i.e. correlators with
linear and second order fields, to quantify the two new counterterms in
isolation and to establish consistency with the power spectrum counterterm. By
investigating the fully non-linear bispectrum, $B_{\mathrm{nnn}}$, as well as
the terms $B_{\mathrm{n}11}$ and $B_{\mathrm{n}21}$, we find evidence for the
new counterterms deviating from the shape suggested by the UV-limit of the
relevant bispectrum contributions. We also show that the commonly used
Einstein-de Sitter approximation for the time dependence of the tree-level
bispectrum is insufficient for precise studies of the one-loop bispectrum and
that it is necessary to use $\Lambda$CDM growth factors in order to obtain
meaningful one-loop counterterm constraints. Finally, we also find evidence for
small deviations in the growth factors that arise from time integration
inaccuracies in the $N$-body simulations.
