2023/10/09 by Andrea Lapi, Lumen Boco, Lapi, Andrea +11 · 3 citations
Economics, Econometrics and Finance · Physics and Astronomy · #Complex Systems and Time Series Analysis #Cosmology and Gravitation Theories #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Stochastic processes and financial applications
paper · pdf · doi:10.48550/arxiv.2310.06028
openalex publication_date 2023/10/09 · openalex created_date 2023/10/12 · openalex updated_date 2026/07/28
[abridged] We propose a model of the Universe (dubbed ηCDM) featuring a stochastic evolution of the cosmological quantities, that is meant to render small deviations from homogeneity/isotropy on scales of 30-50 h-1 Mpc at late cosmic times, associated to the emergence of the cosmic web. Specifically, we prescribe that the behavior of the matter/radiation energy densities in different patches of the Universe with such a size can be effectively described by a stochastic version of the mass-energy evolution equation. The latter includes an appropriate noise term that statistically accounts for local fluctuations due to inhomogeneities, anisotropic stresses and matter flows. The evolution of the different patches as a function of cosmic time is rendered via the diverse realizations of the noise term; meanwhile, at any given cosmic time, sampling the ensemble of patches will originate a nontrivial spatial distribution of the cosmological quantities. The overall behavior of the Universe will be obtained by averaging over the patch ensemble. We assume a physically reasonable parameterization of the noise term, gauging it against a wealth of cosmological datasets. We find that, with respect to standard ΛCDM, the ensemble-averaged cosmic dynamics in the ηCDM model is substantially altered in three main respects: (i) an accelerated expansion is enforced at late cosmic times without the need for any additional exotic component (e.g., dark energy); (ii) the spatial curvature can stay small even in a low-density Universe; (iii) matter can acquire an effective negative pressure at late times. We provide predictions for the variance of the cosmological quantities among different patches of the Universe at late cosmic times. Finally, we show that in ηCDM the Hubble-tension is solved, and the cosmic coincidence problem is relieved without invoking the anthropic principle.