Koyama, KazuyaUmeh, ObinnaMaartens, RoyBertacca, Daniele2018-09-042018-09-042018Koyama, K. et al. (2018). The observed galaxy bispectrum from single- eld in ation in the squeezed limit. Journal of Cosmology and Astroparticle Physics, 20180: 0501475-7516http://dx.doi.org/10.1088/1475-7516/2018/07/050http://hdl.handle.net/10566/4016Using 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.enThis is a pre-print version of the article published online at: http://dx.doi.org/10.1088/1475-7516/2018/07/050Fourier spaceGalaxyGalaxy bispectrumSingle-fi eld inflationArticle