The observed galaxy bispectrum from single-field inflation in the squeezed limit
Date
2018Author
Koyama, Kazuya
Umeh, Obinna
Maartens, Roy
Bertacca, Daniele
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Using the consistency relation in Fourier space, we derive the observed galaxy bispectrum from
single- eld in
ation 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 e ective non-
Gaussianity due to general-relativistic lightcone e ects that could mimic a primordial non-Gaussian
signal.