Cosmological constraints from the DESI DR1 Bispectrum Full-Shape and DR2 BAO

Abstract

We present cosmological constraints from DESI DR1 full-shape measurements, including the LRG bispectrum, combined with DESI DR2 BAO data. The analysis accounts for cross-covariance using mocks, while ShapeFit compression mitigates prior volume effects in beyond-$\Lambda$CDM analyses. In $\Lambda$CDM, the DESI1.5 (P+B) analysis yields ${\sigma }_8=0.868\pm 0.026$ and $S_8=0.880\pm 0.028$, compared with ${\sigma }_8=0.822\pm 0.034$ and $S_8=0.827\pm 0.036$ in the previous power-spectrum-only analysis. The marginalized uncertainties are reduced by 24% and 22%, respectively. For $w_0{w}_a$CDM, DESI-only analyses with the bispectrum shift dark energy parameters toward $\Lambda$CDM, consistent with a cosmological constant within $1\sigma$ in the $w_0$--$w_a$ plane. Adding CMB creates a preference for evolving dark energy: DESI+CMB (P+B) shows a $2.8\sigma$ deviation from $\Lambda$CDM. Including DES-Dovekie supernovae alone reduces this to $1.6\sigma$, while the full combination gives $3.1\sigma$. The bispectrum weakens evidence for time-varying dark energy relative to power-spectrum-only analyses. It also enhances sensitivity to massive neutrinos: in DESI-only data, the power-spectrum-only posterior for $\sum m_{\nu }$ is consistent with zero, whereas adding the bispectrum yields $0.26\pm 0.18$ eV and a 95% upper limit of $0.59$ eV, shifting the peak into the positive region. For modified gravity, the bispectrum constrains ${\mu }_0=0.12\pm 0.51$ from DESI-only data, consistent with general relativity.

arXiv comment39 pages, 12 figures, submitted to JCAP