Joint Constraints on the Hubble Constant and Cosmic Baryon Density from Localized Fast Radio Bursts and DESI DR2 Baryon Acoustic Oscillations

Abstract

Fast radio bursts (FRBs) probe free-electron columns along cosmological sightlines through their dispersion measures (DMs), whereas baryon acoustic oscillations (BAO) constrain cosmic expansion geometry through acoustic distance ratios. In this work, we leverage their distinct physical sensitivities to simultaneously determine the Hubble constant ($H_0$) and cosmic baryon density (${\Omega }_{\mathrm{b}}$) without external cosmic microwave background (CMB) or Big Bang nucleosynthesis (BBN) priors. Combining 120 localized FRBs and DESI DR2 BAO, we obtain $H_0=71.4_{-2.5}^{+2.2}\mathrm{km}{\mathrm{s}}^{-1}\mathrm{Mp}{\mathrm{c}}^{-1}$ and ${\Omega }_{\mathrm{b}}=0.0503_{-0.0021}^{+0.0025}$ in $\Lambda$CDM, corresponding to precisions of $3.3\%$ and $4.6\%$, respectively. The inferred $H_0$ is statistically consistent with both SH0ES and CMB, and ${\Omega }_{\mathrm{b}}$ agrees with the joint constraint from BBN and CMB. Adopting IllustrisTNG-based DM distributions and fixing the diffuse-gas baryon fraction tightens the constraint to $H_0=68.8\pm 1.0\mathrm{km}{\mathrm{s}}^{-1}\mathrm{Mp}{\mathrm{c}}^{-1}$, but lowers the central value toward the CMB-inferred value, identifying extragalactic DM modeling as the dominant systematic uncertainty. These results establish FRB-BAO complementarity as a new avenue for simultaneously constraining $H_0$ and ${\Omega }_{\mathrm{b}}$.

arXiv comment15 pages, 4 figures, 5 tables