Bianchi-I f(Q) models constrained by Pantheon+ DESI data bound anisotropy parameter below 0.01
Preprint analysis of anisotropic f(Q) gravity in Bianchi-I spacetime finds observationally viable models with small shear that reproduce late-time acceleration. Distinct phantom-divide behaviors offer future discriminants. Background data alone leave room for detectable anisotropy with next-generation surveys.
The study reformulates the modified field equations for symmetric teleparallel f(Q) gravity into an autonomous dynamical system for two representative functional forms. Parameters are fitted via MCMC to four dataset combinations, yielding consistent posteriors that tightly limit the present-day anisotropy contribution while permitting distinct dark-energy trajectories. Model I crosses the phantom divide and asymptotes to de Sitter; Model II starts phantom and approaches a cosmological-constant-like state near z=0, closely tracking Lambda-CDM expansion history.
Current background data cannot yet distinguish these anisotropic extensions from isotropic f(Q) or standard cosmology, yet the characteristic phantom-crossing signatures remain testable with future surveys such as Euclid or Roman. The work highlights that small residual anisotropy is still allowed without violating observations, reopening questions about early-universe isotropization mechanisms in modified gravity.
A key limitation is reliance on background observables alone; inclusion of growth-rate or weak-lensing data would tighten anisotropy bounds by an order of magnitude. The analysis also assumes power-law or exponential f(Q) forms; broader functional classes could alter the permitted shear range.
Murtaza et al.: DESI year-3 BAO plus Roman SN data will reduce the 95% upper limit on present-day shear parameter below 0.003 by 2028.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2609.04235)
- [2]Supporting Source(https://arxiv.org/abs/2305.18544)