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arXiv · 2604.05095

A generic $ω_b$ tension in early-time solutions to the Hubble tension

Cara Giovanetti
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Abstract

I show that early-time (pre-recombination) solutions to the Hubble tension are generically expected to increase the preferred baryon density $ω_b$. This puts these models in tension with Big Bang Nucleosynthesis (BBN), as measurements of primordial deuterium constrain $ω_b$ at percent level. I show that existing analyses are in tension with the BBN determination of $ω_b$, and that including a likelihood component for primordial deuterium deters two representative models from recovering a high $H_0$.

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Cara Giovanetti. 2026-09-03. A generic $ω_b$ tension in early-time solutions to the Hubble tension. https://doi.org/10.1088/1475-7516%2F2026%2F08%2F074

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