The observed galaxy bispectrum from single-field inflation in the
  squeezed limit
  Using the consistency relation in Fourier space, we derive the observed
galaxy bispectrum from single-field inflation in the squeezed limit, in which
one of the three modes has a wavelength much longer than the other two. This
provides a non-trivial check of the full computation of the bispectrum based on
second-order cosmological perturbation theory in this limit. We show that gauge
modes need to be carefully removed in the second-order cosmological
perturbations in order to calculate the observed galaxy bispectrum in the
squeezed limit. We then give an estimate of the effective non-Gaussianity due
to general relativistic lightcone effects that could mimic a primordial
non-Gaussian signal.
