Cosmology with the galaxy bispectrum multipoles: Optimal estimation and application to BOSS data

Abstract

We present a framework for self-consistent cosmological analyses of the full-shape anisotropic bispectrum, including the quadrupole ($\ensuremath{\ell}=2$) and hexadecapole ($\ensuremath{\ell}=4$) moments. This features a novel window-free algorithm for extracting the latter quantities from data, derived using a maximum-likelihood prescription. Furthermore, we introduce a theoretical model for the bispectrum multipoles (which does not introduce new free parameters), and test both aspects of the pipeline on several high-fidelity mocks, including the PT Challenge suite of gigantic cumulative volume. This establishes that the systematic error is significantly below the statistical threshold, both for the measurement and modeling. As a realistic example, we extract the large-scale bispectrum multipoles from BOSS DR12 and analyze them in combination with the power spectrum data. Assuming a minimal $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, with a BBN prior on the baryon density and a Planck prior on ${n}_{s}$, we can extract the remaining cosmological parameters directly from the clustering data. The inclusion of the unwindowed higher-order ($\ensuremath{\ell}>0$) large-scale bispectrum multipoles is found to moderately improve one-dimensional cosmological parameter posteriors (at the 5%--10% level), though these multipoles are detected only in three out of four BOSS data segments at $\ensuremath{\approx}5\ensuremath{\sigma}$. Combining information from the power spectrum and bispectrum multipoles, the real space power spectrum, and the postreconstructed BAO data, we find ${H}_{0}=68.2\ifmmode\pm\else\textpm\fi{}0.8\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$, ${\mathrm{\ensuremath{\Omega}}}_{m}=0.33\ifmmode\pm\else\textpm\fi{}0.01$ and ${\ensuremath{\sigma}}_{8}=0.736\ifmmode\pm\else\textpm\fi{}0.033$ (the tightest yet found in perturbative full-shape analyses). Our estimate of the growth parameter ${S}_{8}=0.77\ifmmode\pm\else\textpm\fi{}0.04$ agrees with both weak lensing and CMB results. The estimators and data used in this work have been made publicly available.

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