Breaking the Baryon Density\unicodex2013Hubble Constant Degeneracy in Fast Radio Burst Applications with Associated Gravitational Waves

2025/08/20 by Jahns-Schindler, Joscha N., Spitler, Laura G.
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)

paper · doi:10.48550/arxiv.2508.14434

Abstract

Fast Radio Bursts (FRBs) are a unique probe of the cosmos, owing to dispersion caused by free electrons in the intergalactic medium (IGM). Two of the main quantities of interest are degenerate: the density of matter Ω_bf_d outside of galaxies and the Hubble constant H₀. Here, we present a new possibility of breaking the degeneracy without invoking early Universe priors on Ω_b. Assuming some FRBs originate in compact object mergers, the combination of dispersion and luminosity distance from the gravitational wave (GW) can be used to measure Ω_bh²f_d (where h is the dimensionless Hubble constant). We show that this measurement can be combined with the abundant FRBs that have a redshift measurement. This combination breaks the degeneracy with the Hubble constant. We develop a Bayesian framework and forecast that third-generation GW detectors are required to obtain meaningful constraints. We forecast that one year of Einstein Telescope operations can constrain H₀ to ± 6 kms^-1Mpc^-1 and Ω_bh²f_d to ^+0.0015_-0.0016 (68 % credible interval). The method can also be used with luminosity distances obtained through other means than GWs.

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