Bispectrum Supersample Covariance
  Modes with wavelengths larger than the survey window can have significant
impact on the covariance within the survey window. The supersample covariance
has been recognized as an important source of covariance for the power spectrum
on small scales, and it can potentially be important for the bispectrum
covariance as well. In this paper, using the response function formalism, we
model the supersample covariance contributions to the bispectrum covariance and
the cross covariance between the power spectrum and the bispectrum. The
supersample covariances due to the long wavelength density and tidal
perturbations are investigated, and the tidal contribution is a few orders of
magnitude smaller than the density one because in configuration space the
bispectrum estimator involves angular averaging and the tidal response function
is anisotropic. The impact of the super-survey modes is quantified using
numerical measurements with periodic box and subbox setups. For the matter
bispectrum, the ratio between the supersample covariance correction and the
small scale covariance, which can be computed using a periodic box, is roughly
an order of magnitude smaller than that for the matter power spectrum. This is
because for the bispectrum, the small scale non-Gaussian covariance is
significantly larger than that for the power spectrum. For the cross
covariance, the supersample covariance is as important as for the power
spectrum covariance. The supersample covariance prediction with the halo model
response function is in good agreement with numerical results.
