Reanalyzing DESI DR1: 1. $Λ$CDM Constraints from the Power Spectrum and Bispectrum

Abstract: We present the first independent re-analysis of the galaxy clustering data from DESI Data Release 1, utilizing an effective field theory (EFT)-based full-shape model. We analyze the power spectra and bispectra of the public catalogs using a custom-built pipeline based on window-deconvolved quasi-optimal estimators, carefully accounting for all relevant systematic effects. Compared to the official collaboration analysis, we add the galaxy power spectrum hexadecapole and the bispectrum monopole, and also introduce a novel stochastic estimator for fiber collisions, which facilitates robust bispectrum analyses. As a first application, we perform an EFT-based full-shape analysis of the DESI power spectra and bispectra in the context of the standard cosmological model, $\Lambda$CDM. Using external priors on the physical baryon density and the primordial power spectrum tilt, we constrain the matter density fraction to $\Omega_m=0.284\pm 0.011$, the Hubble constant to $h=0.707\pm 0.011$, and the mass fluctuation amplitude to $\sigma_8=0.811\pm 0.030$. The bispectrum has a noticeable effect on parameter estimation: it sharpens the constraints on $\sigma_8$ and $\Omega_m$ by $\approx 10$\% and shifts $\Omega_m$ by $\approx 1\sigma$ towards the Planck $\Lambda$CDM value. Combining our full-shape likelihood with the official DESI DR2 BAO measurements, cosmological parameters shift further towards the \textit{Planck} values, with $\Omega_m=0.296\pm 0.007$, $h=0.688\pm 0.006$, $\sigma_8=0.818\pm 0.029$ (with tighter constraints obtained in joint analyses). Finally, the galaxy bispectrum data dramatically improves measurements of quadratic bias parameters, which are consistent with predictions from halo occupation distribution models. Our work highlights the importance of higher-order statistics and sets the stage for upcoming full-shape analyses of non-minimal cosmological models.