Assessing The Robustness Of Sound Horizon-Free Determinations Of The Hubble Constant

Authors

Tristan L. Smith, Swarthmore CollegeFollow
V. Poulin
T. Simon

Document Type

Article

Publication Date

11-15-2023

Published In

Physical Review D

Abstract

The Hubble tension can be addressed by modifying the sound horizon (r_s) before recombination, triggering interest in early universe estimates of the Hubble constant, H₀, independent of r_s. Constraints on H₀ from an r_s-free analysis of the full shape BOSS galaxy power spectra within Λ CDM were recently reported and used to comment on the viability of physics beyond Λ CDM. Here we demonstrate that r_s-free analyses with current data depend on both the model and the priors placed on the cosmological parameters, such that Λ CDM analyses cannot be used as evidence for or against new physics. We find that beyond-Λ CDM models which introduce additional energy density with significant pressure support, such as early dark energy (EDE) or additional neutrino energy density (ΔN_eff), lead to r_s-free values of H₀ which are larger by 3–4 km/s/Mpc. On the other hand, models which only affect the time of recombination, such as a varying electron mass (Δm_e), produce H₀ constraints similar to Λ CDM. Using BOSS data, constraints from light element abundances, cosmic microwave background (CMB) lensing, a CMB-based prior on the primordial scalar amplitude (A_s), spectral index (n_s), and Ω_m from the Pantheon + Type Ia supernovae dataset, we find that in Λ CDM, H₀ = 64.9 ± 2.2 km/s/Mpc; in EDE, H₀ = 68.7(+3)/(−3.9); in ΔN_eff, H₀ = 68.1(+2.7)/(−3.8); and in Δm_e, H₀ = 64.7(+1.9)/(−2.3). Using a prior on the angular size of the sound horizon at baryon drag from BAO and CMB measurements, these values become in Λ CDM, H₀ = 67.9 ± 1.7; in EDE, H₀ = 72.2(+2.9)/(−3.8); in ΔN_eff, H₀ = 71.5(+2.5)/(−3.3); and in Δm_e, H₀ = 68.0 ± 1.7. With current data, none of the models are in significant tension with SH₀ES, and consistency tests based on comparing H₀ posteriors with and without r_s marginalization are inconclusive with respect to the viability of beyond Λ CDM models.

Comments

This work is freely available courtesy of the American Physical Society.

Recommended Citation

Tristan L. Smith, V. Poulin, and T. Simon. (2023). "Assessing The Robustness Of Sound Horizon-Free Determinations Of The Hubble Constant". Physical Review D. Volume 108, Issue 10. DOI: 10.1103/PhysRevD.108.103525
https://works.swarthmore.edu/fac-physics/529