Investigating Cosmological Models and the Hubble Tension using Localized Fast Radio Bursts

TL;DR

This study uses 24 localized fast radio bursts to compare cosmological models, finding that the simpler $R_h=ct$ universe is statistically favored over flat $ ext{Lambda}$CDM, and provides constraints on the Hubble constant.

Contribution

It introduces a method to compare cosmological models using FRB dispersion measures and redshifts, favoring the $R_h=ct$ universe with Bayesian analysis.

Findings

$R_h=ct$ is favored over flat $ ext{Lambda}$CDM by BIC.

Estimated $H_0$ around 95 km/s/Mpc with large uncertainties.

An upper limit of $H_0<89$ km/s/Mpc at 95"]},

Abstract

We use the dispersion measure (DM) and redshift measurements of 24 localized fast radio bursts (FRBs) to compare cosmological models and investigate the Hubble tension. Setting a flat prior on the DM contribution from the Milky Way's halo, $\mathrm{DM_{halo}^{MW}}\in[5,\;80]\;\mathrm{pc\;cm^{-3}}$, the best fit for flat $\Lambda$CDM is obtained with a Hubble constant $H_0=95.8^{+7.8}_{-9.2}\;\mathrm{km\;s^{-1}\;Mpc^{-1}}$ and a median matter density $\Omega_{\mathrm{m}}\approx0.66$. The best fit for the $R_{\mathrm{h}}=ct$ universe is realized with $H_0=94.2^{+5.6}_{-6.2}\;\mathrm{km\;s^{-1}\;Mpc^{-1}}$. We emphasize that the $H_0$ measurement depends sensitively on the $\mathrm{DM_{halo}^{MW}}$ prior. Since flat $\Lambda$CDM has one more free parameter, $R_{\mathrm{h}}=ct$ is favored by the Bayesian Information Criterion (BIC) with a likelihood of $\sim73\%$ versus $\sim27\%$. Through simulations, we find that if the real cosmology is $\Lambda$CDM, a sample of $\sim1,150$ FRBs in the redshift range $0<z<3$ would be sufficient to rule out $R_{\mathrm{h}}=ct$ at a $3\sigma$ confidence level, while $\sim550$ FRBs would be necessary to rule out $\Lambda$CDM if the real cosmology is instead $R_{\mathrm{h}}=ct$. The required sample sizes are different, reflecting the fact that the BIC imposes a severe penalty on the model with more free parameters. We further adopt a straightforward method of deriving an upper limit to $H_{0}$, without needing to consider the poorly known probability distribution of the DM contributed by the host galaxy. The theoretical DM contribution from the intergalactic medium ($\mathrm{DM_{IGM}}$) at any $z$ is proportional to $H_0$. Thus, requiring the extragalactic $\mathrm{DM_{ext}}$ to be larger than $\mathrm{DM_{IGM}}$ delimits $H_0$ to the upside. Assuming flat $\Lambda$CDM, we have $H_0<89.0\;\mathrm{km\;s^{-1}\;Mpc^{-1}}$ at a 95\% confidence level.