Cosmological analysis of the DESI DR1 Lyman alpha 1D power spectrum

TL;DR

This paper analyzes the DESI DR1 Lyman-alpha flux power spectrum to constrain cosmological parameters, employing an emulator trained on hydrodynamical simulations, and combines results with other cosmological probes to refine constraints on extensions of the standard model.

Contribution

It introduces a new framework using an emulator for the Lyman-alpha flux power spectrum that accounts for astrophysical systematics and combines data with other measurements for improved cosmological constraints.

Findings

Measured the amplitude and slope of the matter power spectrum at z=3.

Constrained N_eff to 3.02 ± 0.10, improving limits on relativistic species.

Sharpened constraints on spectral index running and its running.

Abstract

We present the cosmological analysis of the one-dimensional Lyman-$\alpha$ flux power spectrum from the first data release of the Dark Energy Spectroscopic Instrument (DESI). We capture the dependence of the signal on cosmology and intergalactic medium physics using an emulator trained on a cosmological suite of hydrodynamical simulations, and we correct its predictions for the impact of astrophysical contaminants and systematics, many of these not considered in previous analyses. We employ this framework to constrain the amplitude and logarithmic slope of the linear matter power spectrum at $k_\star=0.009\,\mathrm{km^{-1}s}$ and redshift $z=3$, obtaining $\Delta^2_\star=0.379\pm0.032$ and $n_\star=-2.309\pm0.019$. The robustness of these constraints is validated through the analysis of mocks and a large number of alternative data analysis variations, with cosmological parameters kept blinded throughout the validation process. We then combine our results with constraints from DESI BAO and temperature, polarization, and lensing measurements from Planck, ACT, and SPT-3G to set constraints on $\Lambda$CDM extensions. While our measurements do not significantly tighten the limits on the sum of neutrino masses from the combination of these probes, they sharpen the constraints on the effective number of relativistic species, $N_\mathrm{eff}=3.02\pm0.10$, the running of the spectral index, $\alpha_\mathrm{s}=0.0014\pm0.0041$, and the running of the running, $\beta_\mathrm{s}=-0.0006\pm0.0048$, by a factor of 1.18, 1.27, and 1.90, respectively. We conclude by outlining the improvements needed to fully reach the level of confidence implied by these uncertainties.