2025/06/13 by Carloni, Youri, Luongo, Orlando, Muccino, Marco · 4 citations
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc)
paper · doi:10.48550/arxiv.2506.11531
We propose that the Hubble tension arises due to an unaccounted additional component, that behaves as matter with pressure. We demonstrate that this fluid remains subdominant compared to both dust and radiation throughout nearly the entire universe expansion history. Specifically, the additional fluid satisfies the Zel'dovic limit with a constant equation of state, ωs > 0, and a quite small normalized energy density, Ωs. Accordingly, this component modifies both the sound horizon and the background expansion rate, acting quite differently from early dark energy models, without significantly affecting the other cosmological parameters. To show this, we perform a Monte Carlo Markov chain analysis of our model, hereafter dubbed ΛωsCDM paradigm, using the publicly available CLASS Boltzmann code. Our results confirm the presence of this fluid, with properties that closely resemble those of radiation. We find best-fit values that satisfy ωs \lesssim ωγ and a relative energy density Ωs / Ωγ= 0.45, with ωr and Ωr the equation of state and density of photons, respectively. The effective fluid may be associated with generalized K-essence models or, alternatively, with Proca-type vector fields, albeit we do not exclude a priori more exotic possibilities, i.e., dark radiation, axions, and so on. Physical implications of our results are analyzed in detail, indicating a statistical preference for the ΛωsCDM scenario over the conventional ΛCDM background.