  We study nucleon-nucleon scattering on the lattice at next-to-leading order
in chiral effective field theory. We determine phase shifts and mixing angles
from the properties of two-nucleon standing waves induced by a hard spherical
wall in the center-of-mass frame. At fixed lattice spacing we test model
independence of the low-energy effective theory by computing
next-to-leading-order corrections for two different leading-order lattice
actions. The first leading-order action includes instantaneous one-pion
exchange and same-site contact interactions. The second leading-order action
includes instantaneous one-pion exchange and Gaussian-smeared interactions. We
find that in each case the results at next-to-leading order are accurate up to
corrections expected at higher order.
