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

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, 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 Ωm ≈ 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 (DMIGM) at any z is proportional to H 0. Thus, requiring the extragalactic DMext to be larger than DMIGM 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.

Observational Constraints on Dynamical Dark Energy Models

“…A large number of cosmological models that go beyond the standard ΛCDM scenario with modified dynamics of the expansion of the universe both in early and late times have been considered in order to resolve these tensions. For reviews, see [66][67][68][69][70][71][72][73][74][75][76]. To solve the problems of the ΛCDM model, models with gravity different from general relativity on cosmological scales in the universe, so-called modified gravity (MG) models, have also been proposed [37,[77][78][79][80][81][82][83][84][85][86][87][88].…”

Fast Radio Burst Energy Function in the Presence of DMhost Variation

“…There is no consensus in determining the type of FRB hosts. Nevertheless, the redshift of an FRB can be inferred from its unique host galaxy, which enables valuable cosmological applications as the localized FRBs accumulate in great numbers [14][15][16][17][18][19][20][21][22][23]; see refs. [24,25] for recent reviews.…”