Cosmological N-Body Simulations with a Large-Scale Tidal Field
  In this paper we carry out anisotropic "separate universe" simulations by
including a large-scale tidal field in the N-body code \textsc{gadget}4 using
an anisotropic expansion factor $A_{ij}$. We use the code in a pure
\textit{particle-mesh} (PM) mode to simulate the evolution of 16 realizations
of an initial density field with and without a large-scale tidal field, which
are then used to measure the \textit{response function} describing how the
tidal field influences structure formation in the linear and non-linear
regimes. Together with the previously measured response to a large scale
overdensity, this completely describes the nonlinear matter bispectrum in the
squeezed limit. We find that, contrary to the density response, the tidal
response never significantly exceeds the large-scale perturbation-theory
prediction even on nonlinear scales for the redshift range we discuss. We
develop a simple halo model that takes into account the effect of the tidal
field and compare it with our direct measurement from the anisotropic N-body
simulations.
