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arXiv · 2512.16591

An effective $\boldsymbol{\Lambda}$-Szekeres modelling of the local Universe with Cosmicflows-4

Marco Galoppo·Leonardo Giani·Morag Hills·Aurélien Valade
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Abstract

We develop an effective description of the local cosmic environment, namely, for redshift $z \lesssim 0.1$, to quantify the bias induced by local structure on cosmological observables. Our approach models the metric of the nearby Universe as a superposition of multi-structured $\Lambda$-Szekeres patches, calibrated against the HAMLET peculiar velocity and density field reconstructions of Cosmicflows-4. From this framework we compute the fully inhomogeneous and anisotropic quasilocal expansion field predicted by our model, and use it to assess the impact of local structure on estimates of $H_0$. For this purpose we analyse low-redshift Type Ia supernovae from the Pantheon+ catalogue. We find that accounting for the local structure increases the Hubble tension, yielding a shift in the best-fit value of the Hubble constant of order $\Delta H_0 \approx 0.5\ \mathrm{km\,s^{-1}Mpc^{-1}}$.

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Marco Galoppo, Leonardo Giani, Morag Hills, Aurélien Valade. 2025-12-18. An effective $\boldsymbol{\Lambda}$-Szekeres modelling of the local Universe with Cosmicflows-4. https://doi.org/10.1088/1475-7516%2F2026%2F06%2F096

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