Reanalyzing DESI DR1: 3. Constraints on Inflation from Galaxy Power Spectra & Bispectra

TL;DR

This work constrains primordial non-Gaussianity (PNG) using DESI DR1 power spectra and bispectra across multiple tracers (galaxies and quasars) with a consistent one-loop EFT framework. It demonstrates that including the bispectrum and high-redshift data significantly improves constraints on local PNG, achieving $f_{ m NL}^{\rm loc}=0\pm4$ when combined with Planck, and provides the strongest DESI-based limits to date on multi-field inflation. It also delivers competitive constraints on non-local PNG shapes, reporting $f_{ m NL}^{\rm equil}=719\pm390$ and $f_{ m NL}^{\rm orth}=-200\pm100$ for baseline DESI DR1, with notable improvements when combining DESI with BOSS data. Overall, the study establishes the galaxy bispectrum as a robust probe of early-Universe physics and outlines avenues for further tightening PNG constraints through extended templates and priors.

Abstract

Models of cosmic inflation generically predict a weak but potentially detectable amount of primordial non-Gaussianity (PNG), which can be used to obtain insights into the degrees of freedom during inflation and their interactions. The simplest types of PNG are the local and non-local (equilateral and orthogonal) shapes of the primordial three-point correlators, which are predicted by models with multiple light fields and derivative interactions in single-field inflation, respectively. In this paper we place constraints on local, equilateral, and orthogonal non-Gaussianities using the power spectrum and bispectrum extracted from first public release of the Dark Energy Spectroscopic Instrument (DESI). Our analysis makes use of higher-order clustering information through a consistent effective field theory (EFT) model for both the power spectrum and bispectrum at one-loop order. Using robust scale cuts where the EFT description is valid, we find the following constraints on PNG amplitudes: $f^{\rm loc}_{\rm NL}=-0.1\pm 7.4$, $f^{\rm equil}_{\rm NL}=719\pm 390$, $f^{\rm orth}_{\rm NL}=-200\pm 100$ (at $68\%$ CL). Non-local PNG constraints can be further improved by combining high-redshift DESI with legacy BOSS data and using simulation-based priors on bias parameters, yielding the strongest large-scale structure constraints to date $f^{\rm equil}_{\rm NL}=200\pm 230$, $f^{\rm orth}_{\rm NL}=-24\pm 86$. Our constraint on $f^{\rm loc}_{\rm NL}$ is competitive with the cosmic microwave background (CMB) limit; the combination gives $f^{\rm loc}_{\rm NL}=-0.0\pm 4.1$, $18\%$ stronger than the CMB only result, which represents the strongest bound on multi-field inflation yet obtained.

Figures (5)

• Figure 1: Upper panel: Power spectrum and bispectrum measurements for the DESI DR1 LRG2 sample at $z_{\rm eff}=0.7$. The bispectrum quadrupole measurements are offset vertically for better visibility, and the Poisson shot noise contribution is subtracted from all relevant statistics. The bispectrum dataset includes bins with centers ranging from $k_{\rm min}=0.0075\,h{\text{Mpc}}^{-1}$ to ${k_\text{max}}=0.15\,h{\text{Mpc}}^{-1}$. Lower panel: Bispectrum multipoles for the squeezed ($k_{\rm min} =0.0075\,h{\text{Mpc}}^{-1}$) and equilateral configurations. The measurements are offset horizontally for better visibility.
• Figure 2: As Fig. \ref{['fig:data_lrg2']}, but for the QSO-all sample (including quasars up to $z=3.1$). Here, we set $k_{\rm min} =0.0025\,h{\text{Mpc}}^{-1}$ for the squeezed bispectra in the lower left panel. Since the primary use-case of this sample is for local PNG studies, we omit the power spectrum hexadecapole and bispectrum quadrupole for this sample, and restrict to $k\leq 0.10\,h{\text{Mpc}}^{-1}$.
• Figure 3: Constraints on the local PNG amplitude, $f_{\rm NL}^{\rm loc}$, from various combinations of DESI galaxies and quasars. Much of our constraining power comes from the QSO-all power spectrum (which refers to the full DESI catalog up to $z_{\rm max}=3.1$), with constraints tightening when adding the bispectrum and other galaxy samples. The full DESI constraint (blue) is close to the CMB bound from Planck; their combination (red) yields the tightest constraints on $f_{\rm NL}^{\rm loc}$ obtained to date. Numerical results are given in Tab. \ref{['tab:params']}.
• Figure 4: Constraints on single-field non-local PNG amplitudes from the DESI galaxy and quasar clustering data. Whilst the constraints from the power spectrum (gray) are weak, we find improved results when adding the large-scale bispectrum (blue) and when extending to shorter scales with the one-loop theory (red). Numerical results are given in Tab. \ref{['tab:params']}.
• Figure 5: Constraints on the single-field non-local PNG from DESI galaxy and quasar clustering data at high redshift, $z>0.6$ (DESI-hz), BOSS DR12, and their combination. Simulation-based priors are applied in all three analyses.