Constraining primordial non-Gaussianity from DESI DR1 quasars and Planck PR4 CMB Lensing

We present the first measurement of local-type primordial non-Gaussianity from the cross-correlation between $1.2$ million spectroscopically confirmed quasars from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI) and the Planck PR4 CMB lensing reconstructions. The analysis is performed in three tomographic redshift bins covering $0.8 < z < 3.5$, covering a sky fraction of $\sim 20%$. We adopt a catalog-based pseudo-$C_\ell$ estimator and apply linear imaging weights validated on noiseless mocks. Compared to previous analyses using photometric quasar samples, our results benefit from the high purity of the DESI spectroscopic sample, the reduced noise of PR4 lensing, and the absence of excess large-scale power in the spectroscopic quasar auto-correlation. Fitting simultaneously for the non-Gaussianity parameter $f_{\mathrm{NL}}$ and the linear bias amplitude in each redshift bin, we obtain $f_{\mathrm{NL}} = 2^{+28}{-34}$ for a response parameter $p=1.6$, and $f{\mathrm{NL}} = 6^{+20}{-24}$ for $p=1.0$. These results improve the constraints on $f{\mathrm{NL}}$ by $\sim 35%$ compared to the previous analysis based on the Legacy Imaging Survey DR9. Our results demonstrate the statistical power of DESI quasars for probing inflationary physics, and highlight the promise of future DESI data releases.

💡 Research Summary

This paper presents the first measurement of local‑type primordial non‑Gaussianity (PNG) using the cross‑correlation between 1.2 million spectroscopically confirmed quasars from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI) and the Planck PR4 cosmic microwave background (CMB) lensing maps. The authors split the quasar sample into three tomographic redshift bins covering 0.8 < z < 3.5 and analyse roughly 20 % of the sky. By employing a catalog‑based pseudo‑Cℓ estimator together with linear imaging weights validated on noiseless mocks, they obtain a clean measurement that is largely immune to the large‑scale systematics that typically plague auto‑correlation analyses.

The theoretical framework follows the standard local PNG formalism, where the primordial potential Φ is perturbed as Φ → Φ + fNL(Φ² − ⟨Φ²⟩). This induces a scale‑dependent correction to the linear bias of tracers, Δb(k,z) ∝ fNL bΦ(z) k⁻² TΦ→δ(k,z). The PNG bias bΦ(z) is modeled using the universal relation bΦ(z)=2δc