The Impact of Non-Gaussianity upon Cosmological Forecasts
  The primary science driver for 3D galaxy surveys is their potential to
constrain cosmological parameters. Forecasts of these surveys' effectiveness
typically assume Gaussian statistics for the underlying matter density, despite
the fact that the actual distribution is decidedly non-Gaussian. To quantify
the effect of this assumption, we employ an analytic expression for the power
spectrum covariance matrix to calculate the Fisher information for BAO-type
model surveys. We find that for typical number densities, at $k_\mathrm{max} =
0.5 h$ Mpc$^{-1}$, Gaussian assumptions significantly overestimate the
information on all parameters considered, in some cases by up to an order of
magnitude. However, after marginalizing over a six-parameter set, the form of
the covariance matrix (dictated by $N$-body simulations) causes the majority of
the effect to shift to the "amplitude-like" parameters, leaving the others
virtually unaffected. We find that Gaussian assumptions at such wavenumbers can
underestimate the dark energy parameter errors by well over 50 per cent,
producing dark energy figures of merit almost 3 times too large. Thus, for 3D
galaxy surveys probing the non-linear regime, proper consideration of
non-Gaussian effects is essential.
