Wide-angle effects in the galaxy bispectrum

Abstract: Primordial non-Gaussianities (PNG) leave unique signatures in the bispectrum of the large-scale structure. With upcoming galaxy surveys set to improve PNG constraints by at least one order of magnitude, it is important to account for any potential contamination. In our work we show how to include wide-angle effects into the 3-dimensional observed galaxy bispectrum. We compute the leading wide-angle corrections to the monopole, finding that they could mimic local PNG with an amplitude of $f_{\rm NL} = \mathcal{O}\left( 0.1 \right)$. We also compute the dipole induced by wide-angle effects, whose amplitude is a few-percent of the flat-sky monopole. We estimate that wide-angle effects in the monopole can be safely neglected for survey volumes of the order of $8~\mathrm{Gpc}^3 h^{-3}$, while the dipole can start being detected from surveys probing volumes larger than $50~\mathrm{Gpc}^3 h^{-3}$. Our formalism can be readily adapted to realistic survey geometries and to include relativistic effects, which may become relevant at high redshifts.