Cosmological inference from a joint DESI DR1 full-shape power spectrum and bispectrum analysis

The galaxy bispectrum directly probes the non-linear gravitational evolution of large-scale structure and can break parameter degeneracies that remain in power-spectrum analyses.

This work presents a joint full-shape cosmological analysis of three luminous red galaxy (LRG) redshift bins and the quasar (QSO) sample from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1). The redshift-space power spectrum is modeled at one loop, and the tree-level bispectrum is modeled within the Effective Field Theory of large-scale structure (EFT of LSS). The bispectrum is decomposed in the Tripolar Spherical Harmonics basis, which allows the convolution with the survey window function to be formulated as a direct linear transformation of the theoretical multipoles.

The power-spectrum constraints agree well with the official DESI DR1 full-modelling results. Including the bispectrum monopole in the inference substantially improves constraints on the cold dark matter density and the amplitude of matter fluctuations by 9–18% and 8–20%, respectively, in the individual-tracer analyses. The corresponding reductions are 15% and 10% for the combined LRG sample, and 6% and 4% when all tracers are combined. In a restricted test using the first LRG bin, the bispectrum quadrupole changes the marginalised uncertainties by only a few percent.

Extending the analysis to w0waCDM substantially broadens the cosmological posteriors, while the bispectrum produces only a mild change in the allowed dark-energy parameter region, which remains sensitive to the adopted prior ranges. Overall, the results demonstrate the potential of higher-order clustering statistics to improve cosmological constraints and provide a framework for incorporating the bispectrum into full-shape analyses of current and future spectroscopic galaxy surveys.