A tale of two (or more) h's

Samuel Brieden, Héctor Gil-Marín, Licia Verde

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We use the large-scale structure galaxy data (LSS) from the BOSS and eBOSS surveys, in combination with abundances information from Big Bang Nucleosynthesis (BBN) to measure two values of the Hubble expansion rate, H0=100h[kms−1Mpc−1], each of them based on very different physical processes. One is a (traditional) late-time-background measurement based on determining the BAO scale and using BBN abundances on baryons for calibrating its absolute size (BAO+BBN). This method anchors H0 to the (standard) physics of the sound horizon scale at pre-recombination times. The other is a newer early-time based measurement associated with the broadband shape of the power spectrum. This second method anchors H0 to the physics of the matter-radiation equality scale, which also needs BBN information for determining the suppression of baryons in the power spectrum shape (shape+BBN). Within the ΛCDM model, we find very good consistency among these two H0's: BAO+BBN (+growth) delivers H0=67.42+0.88−0.94 (67.37+0.86−0.95) km s−1Mpc−1 , whereas the shape+BBN (+growth) delivers H0=70.1+2.1−2.1 (70.1+1.9−2.1) km s−1 Mpc−1, where "growth" stands for information from the late-time-perturbations captured by the growth of structure parameter. These are the tightest sound-horizon free H0 constraints from LSS data to date. As a consequence to be viable, any ΛCDM extension proposed to address the so-called "Hubble tension" needs to modify consistently not only the sound horizon scale physics, but also the matter-radiation equality scale, in such a way that both late- and early-based H0's return results mutually consistent and consistent with the high H0 value recovered by the standard cosmic distance ladder (distance-redshift relation) determinations.
Original languageEnglish
Article number023
Pages (from-to)1-43
Number of pages43
JournalJournal of Cosmology and Astroparticle Physics (JCAP)
Issue number4
Publication statusPublished - 11 Apr 2023

Keywords / Materials (for Non-textual outputs)

  • baryon acoustic ascillations
  • cosmological parameters from LSS
  • power spectrum
  • redshift surveys


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