An $n$-th order Lagrangian Forward Model for Large-Scale Structure
  A forward model of matter and biased tracers at arbitrary order in Lagrangian
perturbation theory (LPT) is presented. The forward model contains the complete
LPT displacement field at any given order in perturbations, as well as all
relevant bias operators at that order and leading order in derivatives. The
construction is done for any expansion history and does not rely on the
Einstein-de Sitter approximation. A large subset of higher-derivative bias
operators is also included. As validation test, we compare the $n$LPT-predicted
matter density field and that from N-body simulations using the same initial
conditions. For simulations using a cutoff in the initial conditions, we find
subpercent agreement up to scales of $k\sim 0.2 h\,{\rm Mpc}^{-1}$. We also
find subpercent agreement with full simulations without cutoff, both for the
power spectrum and nonlinear $\sigma_8$-inference, when allowing for the
effective sound speed. The application to biased tracers (halos) has already
been presented in a recent paper (arXiv:2009.14176).
