Constraining Cosmological Physics with DESI BAO Observations

TL;DR

This work leverages the DESI year-one BAO measurements, in combination with BK18 CMB data and SN Pantheon+, to probe physics beyond the standard $\Lambda$CDM model across inflation, modified gravity, annihilating dark matter, interacting dark energy, and sterile neutrinos. Using a joint Bayesian analysis with Planck 2018 data, DESI BAO, and other probes, the study derives a $2\sigma$ lower bound on the tensor-to-scalar ratio $r$ and finds a mild to moderate preference for beyond-GR gravity, while tightening constraints on dark-matter annihilation, DM–DE interactions, and sterile-neutrino parameters. The results show $r_{0.05}=0.0176^{+0.0070}_{-0.0130}$ (1σ) and a $2σ$ lower bound, $ _s\approx0.970$, and a $2.4\sigma$ deviation from GR via $S_0=\mu_0+0.4\eta_0$, with $\mu_0-1$ and $\eta_0-1$ compatible with GR within uncertainties. For the dark sector, $\epsilon_0 f_d<0.241$ (2σ) and $\beta\approx0.065^{+0.056}_{-0.050}$ (1σ) suggest possible DM→DE energy transfer, while sterile-neutrino hints yield $N_{\rm eff}=3.16^{+0.26}_{-0.11}$ and $m^{\rm eff}_{\nu,\mathrm{sterile}}<0.52$ eV (2σ). Overall, DESI BAO strengthens tests of inflation, gravity, and neutrino physics on cosmological scales and will enable even tighter constraints with future data releases.

Abstract

The DESI year one observations can help probe new physics on cosmological scales. In light of the latest DESI BAO measurements, we constrain five popular cosmological scenarios including inflation, modified gravity, annihilating dark matter and interacting dark energy. Using a data combination of BICEP/Keck array, cosmic microwave background and DESI, we obtain the $1σ$ and $2σ$ constraints on the tensor-to-scalar ratio $r_{0.05}= 0.0176^{+0.0070}_{-0.0130}$ and $r_{0.05}=0.018^{+0.020}_{-0.017}$ indicating a beyond $2σ$ evidence of primordial gravitational waves. Using the combination of cosmic microwave background and DESI, we find a $2.4σ$ evidence for gravitational theories beyond the general relativity, shrink the dark matter annihilation cross-section by $12\%$ relative to cosmic microwave background, obtain a $1.3σ$ hint of the positive interaction between dark matter and dark energy implying that energy may be transferred from dark matter to dark energy in the dark sector of the universe, and give a clue of massive sterile neutrinos via the $2σ$ constraint on the effective number of relativistic degrees of freedom $N_{eff}=3.16^{+0.26}_{-0.11}$ and the effective mass $m^{eff}_{ν, sterile}<0.52$ eV. Future DESI observations could go a step further to explore the nature of inflation, dark matter, dark energy and neutrinos, and test the validity of general relativity on cosmological scales.

Figures (6)

• Figure 1: The two-dimensional marginalized posterior distributions of the parameter pair ($n_s$, $r_{0.002}$) from CMB (green), BK18+CMB+SDSS (grey) and BK18+CMB+DESI (blue) observations in the $\Lambda$+$r$ scenario, compared to the theoretical predictions of selected inflationary models. Here $\phi$ denotes the inflationary scalar field and $N\equiv{\rm ln}a$ is the e-folding number.
• Figure 2: The two-dimensional marginalized posterior distributions of the parameter pair ($\mu_0$, $\eta_0$) from CMB (red) and CMB+DESI (blue) observations in the MG scenario. $S_0$ acts as a signal parameter to measure the deviation from the GR. The red and blue points denote the best fit value and $2\sigma$ limits of $S_0$, respectively. Similarly, the red and blue lines are the best fit line and $2\sigma$ boundaries when using the fitting formula $S_0=\mu_0+0.4\eta_0$, respectively. The magenta dashed line corresponds to $\eta_0=0$ and the cross point between black dashed lines represents the GR case.
• Figure 3: The two-dimensional marginalized posterior distributions of the cosmological parameters from CMB (red) and CMB+DESI (blue) observations in the ADM scenario.
• Figure 4: CMB+DESI constraints on the dark matter mass and annihilation cross-section. We assume the dark matter annihilation efficiency $\epsilon_0 f_{\rm d}=0.241$ and vary the transferred energy fraction $f_{\rm d}$. As a comparison, the dashed line denotes the Planck CMB bound assuming $\epsilon_0 f_{\rm d}=0.28$.
• Figure 5: The two-dimensional marginalized posterior distributions of the parameter pair $(\beta, \Omega_m)$ from CMB (green), CMB+DESI (red) and CMB+DESI+SN (blue) observations in the IDE scenario. The vertical dashed line denote the $\Lambda$CDM case corresponding to $\beta=0$.