Cosmology without window functions. II. Cubic estimators for the galaxy bispectrum

When analyzing the galaxy bispectrum measured from spectroscopic surveys, it is imperative to account for the effects of nonuniform survey geometry. Conventionally, this is done by convolving the theory model with the window function; however, the computational expense of this prohibits full exploration of the bispectrum likelihood. In this work, we provide a new class of estimators for the unwindowed bispectrum, a quantity that can be straightforwardly compared to theory. This builds upon the work of Philcox [Phys. Rev. D 103, 103504 (2021), 10.1103/PhysRevD.103.103504] for the power spectrum and comprises two parts (both obtained from an Edgeworth expansion): a cubic estimator applied to the data and a Fisher matrix, which deconvolves the bispectrum components. In the limit of weak non-Gaussianity, the estimator is minimum variance; furthermore, we give an alternate form based on Feldman-Kaiser-Peacock weights that is close to optimal and easy to compute. As a demonstration, we measure the binned bispectrum monopole of a suite of simulations using both conventional estimators and our unwindowed equivalents. Computation times are comparable, except that the unwindowed approach requires a Fisher matrix, computable in an additional O (100 ) CPU hours. Our estimator may be straightforwardly extended to measure redshift-space distortions and the components of the bispectrum in arbitrary separable bases. The techniques of this work will allow the bispectrum to straightforwardly be included in the cosmological analysis of current and upcoming survey data.