Full-Shape analysis of the power spectrum and bispectrum of DESI DR1 LRG and QSO samples

Abstract

We present the first joint analysis of the power spectrum and bispectrum using the Data Release 1 (DR1) of the Dark Energy Spectroscopic Instrument (DESI), focusing on Luminous Red Galaxies (LRGs) and quasars (QSOs) across a redshift range of 0.4 ≤ z ≤ 2.1. By combining the two- and three-point statistics, we are able to partially break the degeneracy between the logarithmic growth rate, f(z), and the amplitude of dark matter fluctuations, σs8(z), which cannot be measured separately in analyses that only involve the power spectrum. In comparison with the (fiducial) Planck ΛCDM cosmology we obtain f/ffid = {0.888-0.089+0.186,0.977-0.220+0.182,1.030-0.085+0.368}, σs8/σfids8 = {1.224-0.133+0.091,1.071-0.163+0.278,1.00 0-0.223+0.088} respectively for the three LRG redshift bins, corresponding to a cumulative 10.1% constraint on f, and of 8.4% on σs8, including the systematic error budget. Additionally, we obtain constraints for the ShapeFit compressed parameters describing the isotropic scaling parameter, αiso(z), the Alcock-Paczyński parameter, αAP(z), the combined growth of structure parameter fσs8(z), and the combined shape parameter m(z)+n(z). Their cumulative constraints from our joint power spectrum-bispectrum analysis are respectively σαiso = 0.9% (9% improvement with respect to our power spectrum-only analysis); σαAP = 2.3% (no improvement with respect to power spectrum-only analysis, which is expected given that the bispectrum monopole has no significant anisotropic signal); σfσs8 = 5.1% (9% improvement); σm+n = 2.3% (11% improvement). These results are fully consistent with the main DESI power spectrum analysis, demonstrating the robustness of the DESI cosmological constraints, and compatible with Planck ΛCDM cosmology.