Expanding covariant cosmography of the local universe: incorporating the snap and axial symmetry

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Date

2025

Journal Title

Journal ISSN

Volume Title

Publisher

Institute of Physics

Abstract

Studies show that the model-independent, fully non-perturbative covariant cosmographic approach is suitable for analyzing the local Universe (z ≲ 0.1). However, accurately characterizing large and inhomogeneous mass distributions requires the fourth-order term in the redshift expansion of the covariant luminosity distance dL (zn ). We calculate the covariant snap parameter S and its spherical harmonic multipole moments using the matter expansion tensor and the evolution equations for lightray bundles. The fourth-order term adds 36 degrees of freedom, since the highest independent multipole of the snap is the 32-pole (dotriacontapole) (ℓ=5). Including this term helps to de-bias estimations of the covariant deceleration parameter. Given that observations suggest axially symmetric anisotropies in the Hubble diagram for z ≲ 0.1 and theory shows that only a subset of multipoles contributes to the signal, we demonstrate that only 12 degrees of freedom are needed for a model-independent description of the local universe. We use an analytical axisymmetric model of the local Universe, with data that matches the Zwicky Transient Facility survey, in order to provide a numerical example of the amplitude of the snap multipoles and to forecast precision.

Description

Keywords

Cosmic flows, Cosmological parameters from LSS, Cosmological simulations, Axial symmetry, Covariant deceleration

Citation

Kalbouneh, B., Santiago, J., Marinoni, C., Maartens, R., Clarkson, C. and Sarma, M., 2025. Expanding covariant cosmography of the local universe: incorporating the snap and axial symmetry. Journal of Cosmology and Astroparticle Physics, 2025(02), p.076.