Cosmic propagators at two-loop order
  We explore the properties of two-point cosmic propagators when Perturbation
Theory (PT) loop corrections are consistently taken into account. We show in
particular how the interpolation scheme proposed in arXiv:1112.3895 can be
explicitly used up to two-loop order introducing the notion of regular parts
for the contributing terms. Extending the one-loop results, we then derive and
give semi analytical forms of the two-loop contributions for both the cosmic
density and velocity propagators. These results are tested against numerical
simulations and shown to significantly improve upon one-loop results for
redshifts above 0.5. We found however that at lower redshift two-loop order
corrections are too large partly due to a strong sensitivity of those terms to
the small scale modes. We show that this dependence is expected to be even
larger for higher order loop corrections both from theoretical investigations
and numerical tests, the latter obtained with Monte Carlo evaluations of the
three-loop contributions. This makes small-scale regularization schemes
necessary for the use of such higher order corrections.
