The large-scale general-relativistic correction for Newtonian mocks
  We clarify the subtle issue of finding the correct mapping of Newtonian
simulations to light-cone observables at very large distance scales. A faithful
general-relativistic interpretation specifies a gauge, i.e. a chart that
relates the simulation data to points of the space-time manifold. It has
already been pointed out that the implicit gauge choice of Newtonian
simulations is indeed different from the Poisson gauge that is commonly adopted
for relativistic calculations, the difference being most significant at large
scales. It is therefore inconsistent, for example, to predict weak-lensing
observables from simulations unless this gauge issue is properly accounted for.
Using perturbation theory as well as fully relativistic N-body simulations we
quantify the systematic error introduced this way, and we discuss several
solutions that would render the calculations relativistically self-consistent.
