  We put forward and test a simple description of multi-point propagators (MP),
which serve as building-blocks to calculate the nonlinear matter power
spectrum. On large scales these propagators reduce to the well-known kernels in
standard perturbation theory, while at smaller scales they are suppresed due to
nonlinear couplings. Through extensive testing with numerical simulations we
find that this decay is characterized by the same damping scale for both two
and three-point propagators. In turn this transition can be well modeled with
resummation results that exponentiate one-loop computations. For the first
time, we measure the four components of the non-linear (two-point) propagator
using dedicated simulations started from two independent random Gaussian fields
for positions and velocities, verifying in detail the fundamentals of
propagator resummation.
  We use these results to develop an implementation of the MP-expansion for the
nonlinear power spectrum that only requires seconds to evaluate at BAO scales.
To test it we construct six suites of large numerical simulations with
different cosmologies. From these and
  LasDamas runs we show that the nonlinear power spectrum can be described at
the ~ 2% level at BAO scales for redshifts in the range [0-2.5]. We make a
public release of the MPTbreeze code with the hope that it can be useful to the
community.
