Nonlinear Information from DESI Luminous Red Galaxies: An Emulator-Based Analysis of Pre- and Post-Reconstruction Power Spectra

Abstract

We present joint measurements of the pre- and post-reconstruction power spectra, $P_{\mathrm{pre}}$ and $P_{\mathrm{post}}$, together with their cross-power spectrum, $P_{\mathrm{cross}}$, for the Luminous Red Galaxies (LRGs) in the DESI Data Release 1 (DR1). We jointly analyse these observables with an emulator-based full-shape modeling framework, thereby, for the first time, we extract complementary nonlinear information from the galaxy density field before and after reconstruction in real survey data. Specifically, including $P_{\mathrm{post}}$ and $P_{\mathrm{cross}}$ in addition to $P_{\mathrm{pre}}$ (hereafter $P_{\mathrm{all}}$) yields an improvement of approximately $18$-$27\%$ in the $\ddot{I}{ƒ}_8$ constraint in both $\hat{I}›$CDM and $w$CDM, depending on the redshift bin, relative to the $P_{\mathrm{pre}}$-only analysis with the cosmic microwave background distance priors (hereafter CMB). In $w$CDM, the joint CMB+$P_{\mathrm{all}}$ analysis can tighten the constraints on $w$ by approximately $5$-$15\%$ across the two LRG redshift bins, compared to the CMB+$P_{\mathrm{pre}}$ combination. Further incorporating the Type Ia supernova dataset and comparing the cosmological constraints in $w$CDM from each individual power-spectrum component with those from the full combination, we find that $P_{\mathrm{all}}$ consistently provides the tightest constraints. From the joint CMB+$P_{\mathrm{all}}$+DES-Dovekie dataset, we obtain $\hat{I}{\text{c◯}}_m=0.314\pm 0.0048$ and $w=-0.988\pm 0.023$ for the \texttt{LRG1} sample, and $\hat{I}{\text{c◯}}_m=0.318\pm 0.0046$ and $w=-0.988\pm 0.025$ for \texttt{LRG2}. These results demonstrate that combining pre- and post-reconstruction power spectra with their cross-correlation enables DESI to harvest additional nonlinear information, leading to tighter constraints on cosmological parameters.

19+6 pages