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

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, DM halo MW ∈ [ 5 , 80 ] pc cm − 3 , the best fit for flat ΛCDM is obtained with a Hubble constant H 0 = 95.8 − 9.2 + 7.8 km s − 1 Mpc − 1 and a median matter density Ω_m ≈ 0.66. The best fit for the R _h = ct universe is realized with H 0 = 94.2 − 6.2 + 5.6 km s − 1 Mpc − 1 . We emphasize that the H ₀ measurement depends sensitively on the DM halo MW prior. Since flat ΛCDM has one more free parameter, R _h = ct is favored by the Bayesian Information Criterion (BIC) with a likelihood of ∼73% versus ∼27%. Through simulations, we find that if the real cosmology is ΛCDM, a sample of ∼1150 FRBs in the redshift range 0 < z < 3 would be sufficient to rule out R _h = ct at a 3σ confidence level, while ∼550 FRBs would be necessary to rule out ΛCDM if the real cosmology is instead R _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 (DM_IGM) at any z is proportional to H ₀. Thus, requiring the extragalactic DM_ext to be larger than DM_IGM delimits H ₀ to the upside. Assuming flat ΛCDM, we have H ₀ < 89.0 km s⁻¹ Mpc⁻¹ at a 95% confidence level.