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Cosmic baryon census with fast radio bursts and gravitational waves

Ji-Guo Zhang, Ji-Yu Song, Ze-Wei Zhao, Wan-Peng Sun, Jing-Fei Zhang, Xin Zhang

TL;DR

The paper tackles the missing baryon problem and the $H_0$ tension by formulating a late-Universe probe that jointly uses fast radio burst dispersion measures and gravitational-wave standard siren distances to infer the cosmic baryon density $Ω_{ m b}$ without assuming a fixed $H_0$. It analyzes 104 localized FRBs and 47 GW events in a unified Bayesian framework, marginalizing over FRB DM nuisance parameters and, in some runs, GW population parameters. The main result is $Ω_{ m b}=0.0488±0.0064$ (1σ), independent of $H_0$, which is consistent with early-Universe CMB+BBN constraints, while the inferred $H_0$ is driven by GW data. The study demonstrates that FRB and GW synergy yields a robust, calibration-free baryon census at low redshift and foreshadows a powerful low-redshift cosmological probe as future FRB and GW samples grow.

Abstract

The cosmic baryon density fraction ($Ω_{\rm b}$) is intrinsically correlated with the Hubble constant ($H_0$) through the critical density of the Universe. In the context of the decade-long $H_0$ tension, the significant discrepancy between early- and late-Universe measurements of $H_0$ implies that fixing its value or imposing an external prior could bias the baryon census. To address this concern, we construct a late-Universe probe framework that unifies fast radio bursts (FRBs) and gravitational-wave (GW) standard sirens, which can respectively resolve the missing baryon problem and the $H_0$ tension through their dispersion measures and absolute luminosity distances. By combining $104$ localized FRBs with $47$ GW events, we obtain an $H_0$-free measurement of $Ω_{\rm b}=0.0488\pm0.0064$ ($1σ$), in concordance with early-Universe observations of CMB + BBN. Although the current precision ($\sim 13\%$) is limited by sample size, the growing detections of both FRBs and GWs will make their synergy a powerful probe of low-redshift cosmology.

Cosmic baryon census with fast radio bursts and gravitational waves

TL;DR

The paper tackles the missing baryon problem and the tension by formulating a late-Universe probe that jointly uses fast radio burst dispersion measures and gravitational-wave standard siren distances to infer the cosmic baryon density without assuming a fixed . It analyzes 104 localized FRBs and 47 GW events in a unified Bayesian framework, marginalizing over FRB DM nuisance parameters and, in some runs, GW population parameters. The main result is (1σ), independent of , which is consistent with early-Universe CMB+BBN constraints, while the inferred is driven by GW data. The study demonstrates that FRB and GW synergy yields a robust, calibration-free baryon census at low redshift and foreshadows a powerful low-redshift cosmological probe as future FRB and GW samples grow.

Abstract

The cosmic baryon density fraction () is intrinsically correlated with the Hubble constant () through the critical density of the Universe. In the context of the decade-long tension, the significant discrepancy between early- and late-Universe measurements of implies that fixing its value or imposing an external prior could bias the baryon census. To address this concern, we construct a late-Universe probe framework that unifies fast radio bursts (FRBs) and gravitational-wave (GW) standard sirens, which can respectively resolve the missing baryon problem and the tension through their dispersion measures and absolute luminosity distances. By combining localized FRBs with GW events, we obtain an -free measurement of (), in concordance with early-Universe observations of CMB + BBN. Although the current precision () is limited by sample size, the growing detections of both FRBs and GWs will make their synergy a powerful probe of low-redshift cosmology.

Paper Structure

This paper contains 13 sections, 8 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Data and methodology
  3. Localized FRB data
  4. GW standard siren data
  5. Joint analysis of FRB and GW data
  6. Results and discussions
  7. Main results
  8. Impact of FRB model parameters
  9. Impact of GW model parameters
  10. Conclusion
  11. Acknowledgments
  12. Constraints on H0 and DM parameters
  13. FRB data

Figures (4)

  • Figure 1: Normalized posterior distributions of $\Omega_{\rm b}~$ from 104 FRBs (orange) and 104 FRBs + 47 GWs (indigo). The median and $1\sigma$ credible interval from FRB + GW is $\Omega_{\rm b} = 0.0488 \pm 0.0064$, marginalized over $f_{\rm d}$ and empirical DM model parameters. The errorbars in different colors and linestyles are shown under different assumptions: FRB + $H_0$ (Planck18 prior) and FRB + $H_0$ (SH0ES prior) adopt Gaussian priors on $H_0$ from Planck18 2020Planck and SH0ES Riess:2021jrx, respectively; FRB (TNG) + GW and FRB (TNG + $f_{\rm d}(z)$) + GW adopt priors on empirical DM model parameters from the IllustrisTNG simulation Zhang:2020mgqZhang:2020xoc and on $f_{\rm d}$ from the redshift-dependent form of Macquart20 Macquart:2020lln, respectively. The blue, gray, and red shaded bands show the results from CMB + BBN Cooke:2017cwo, Macquart20, and Yang22 Yang:2022ftm, respectively. Note that Yang22 adopts the TNG prior, a flat prior on $H_0$$\in$$\mathcal{U}(67, 73)$ km s$^{-1}$ Mpc$^{-1}$, and $f_{\rm d}=0.82$. All results are at the $1\sigma$ level.
  • Figure 2: Posterior distributions ($1\sigma$ and $2\sigma$ credible regions) for $\Omega_{\rm b}$ and $\Omega_{\rm b} h_{70}$ versus $H_0$, $f_{\rm d}$, $F$, $\mu_{\rm host}$, and $\sigma_{\rm host}$, using FRB (orange) and FRB + GW (indigo) data. The correlation coefficient $r$ is labeled in each panel to quantify parameter degeneracies. Note that $H_0$ is in units of km s$^{-1}$ Mpc$^{-1}$.
  • Figure 3: Posterior distributions ($1\sigma$ and $2\sigma$ credible regions) for $\Omega_{\rm m}$, $H_0$, and the typical GW population parameter $\mu_{g}$ using FRB + GW data. Two cases are shown: GW parameters fixed within the PowerLaw + Peak model (indigo) and the parameters allowed to vary freely and marginalised over (gray). The dotted lines indicate the median values of each posterior, except for $\mu_g$ in the GW-parameter-fixed case, where the dotted line marks the prior value $\mu_g = 32.27$ adopted following Ref. LIGOScientific:2021aug. Note that $H_0$ is in units of km s$^{-1}$ Mpc$^{-1}$.
  • Figure 4: Same as Fig. \ref{['Fig:1']} but for posterior distribution of $H_0$. The median and $1\sigma$ credible interval from FRB + GW is $H_0 = 71.6^{+4.4}_{-8.6}$ km s$^{-1}$ Mpc$^{-1}$. The orange and black errorbars correspond to constraints from FRB + $\Omega_{\rm b}h^2$ (BBN prior Cooke:2017cwo) and GW data alone, respectively. The green, yellow, red, and gray shaded bands denote the results from Planck18 2020Planck, SH0ES Riess:2021jrx), Wu22 Wu:2021jyk, and James22 James:2022dcx, respectively. Note that Wu22 adopts the TNG prior, and both Wu22 and James22 adopt $\Omega_{\rm b}h^2$ priors from BBN Cooke:2017cwo and CMB 2020Planck, respectively. All results are at $1\sigma$ uncertainty.