Contributions to the Dark Matter 3-Pt Function from the Radiation Era
  We consider the contribution to the three-point function of matter density
fluctuations from nonlinear growth after modes re-enter the horizon, and
discuss effects that must be included in order to predict the three-point
function with an accuracy comparable to primordial nongaussianities with f_NL ~
few. In particular, we note that the shortest wavelength modes measured in
galaxy surveys entered the horizon during the radiation era, and, as a result,
the radiation era modifies their three-point function by a magnitude equivalent
to f_NL ~ O(4). On longer wavelengths, where the radiation era is negligible,
we find that the corrections to the nonlinear growth from relativistic effects
become important at the level f_NL ~ few. We implement a simple method for
numerically calculating the three-point function, by solving the second-order
equations of motion for the perturbations with the first order perturbations
providing a source.
