Constraints on the baryon density from fast radio bursts using a non-parametric reconstruction of the Hubble parameter

TL;DR

This paper uses 130 localized fast radio bursts and a neural-network reconstructed Hubble parameter to precisely measure the baryon density, aligning with early-Universe estimates and demonstrating future potential.

Contribution

It introduces a non-parametric method combining FRB data and neural-network H(z) reconstruction to constrain baryon density and host galaxy properties.

Findings

Measured baryon density consistent with Big Bang Nucleosynthesis and Planck CMB.

Mock data suggests future FRB samples can reduce uncertainty to sub-percent levels.

Method provides a robust low-redshift probe of baryon density.

Abstract

In this study, we use a sample of 130 well-localized fast radio bursts (FRBs) to constrain the physical baryon density $\Omega_{\rm b}h^2$, and the astrophysical contribution from host galaxies. The cosmological dependence entering the intergalactic dispersion measure is described through a non-parametric reconstruction of the Hubble parameter $H(z)$ obtained from cosmic chronometer data using the \texttt{ReFANN} neural-network framework, independently of the FRB sample. Within a Bayesian analysis, we jointly infer $\Omega_{\rm b}h^2$ and the parameters of a log-normal host-galaxy distribution, namely its median $e^\mu$ and logarithmic scatter $\sigma_{\rm host}$, using both real FRB data and a mock catalog. For the real sample, we obtain $\Omega_{\rm b}h^2=0.02236\pm0.00090$, $e^\mu=178.15^{+16.51}_{-16.97}~\mathrm{pc}\,\mathrm{cm}^{-3}$, and $\sigma_{\rm host}=0.794^{+0.064}_{-0.067}$. For the mock catalog, we find $\Omega_{\rm b}h^2=0.02248\pm0.00018$, $e^\mu=182.36^{+6.83}_{-6.48}~\mathrm{pc}\,\mathrm{cm}^{-3}$, and $\sigma_{\rm host}=0.711^{+0.024}_{-0.025}$. The baryon density constraint from the real FRB sample is in excellent agreement with both Big Bang Nucleosynthesis and Planck CMB determinations, differing from their central values by only $\simeq 0.05\%$. The mock analysis further illustrates the potential of future FRB samples, reducing the uncertainty on $\Omega_{\rm b}h^2$ to the sub-percent level while remaining statistically consistent with early-Universe constraints. Our findings show that combining FRB dispersion measures with a non-parametric reconstruction of the expansion history provides a robust pathway to constrain both cosmological and astrophysical parameters, establishing FRBs as a complementary low-redshift probe of the baryon density.