Work

How isotropic is dark energy?

Year: 2026

Type: article

Abstract: Tensions in late-time expansion data have renewed interest in models beyond Λ CDM . We ask: Working in Bianchi I, we allow time-dependent anisotropic stress and introduce a parametrization that enforces a vanishing line-of-sight integral of the shear, thereby satisfying the CMB integrated Sachs–Wolfe quadrupole bound by construction. Using Pantheon + SH 0 ES SNe together with Dark Energy Spectroscopic Instrument (DESI) baryon acoustic oscillation (BAO) distances, single-bin (constant) and five-bin anisotropic models improve the fit over w CDM by Δ ( − 2 ln L iso ) = 14.8 and 26.6, respectively, but both violate the quadrupole constraint. In contrast, a five-bin constrained model achieves Δ ( − 2 ln L iso ) = 15.4 while remaining compatible with the quadrupole limit. The fit improvement arises from two sources: capturing directional structure in the Pantheon + SNe data, and partially alleviating the tension between the SH0ES H 0 value and DESI BAO distances.

Source: Physical review. D/Physical review. D.

DOI: 10.1103/7195-wl39

Authors: Richard A. Battye, Adam Moss

Institutions: University of Manchester, University of Nottingham

Language: English

Topic: Cosmology and Gravitation Theories

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: hybrid

Funder: Science and Technology Facilities Council

Award: The Cosmology of the Early and Late Universe