Correlated Directional Anisotropy in Pantheon+ Supernovae and DESI Baryon Acoustic Oscillations

This work reports evidence for correlated directional anisotropy in low-to-intermediate redshift cosmological observations. Using Type Ia supernovae from the Pantheon+ compilation and baryon acoustic oscillation measurements from DESI, a consistent preferred expansion axis is identified near Galactic coordinates (l, b) ≈ (200°, –70°), close to the CMB Cold Spot. A dipole-modulated residual analysis reveals enhanced expansion along this direction, supported independently by both probes.

Robustness checks include a full-sky directional scan, bootstrap resampling with 10,000 iterations, and jackknife removal across sky sectors. The signal persists under standard systematic tests, indicating it is unlikely to result from survey geometry or calibration effects. The results suggest a modest deviation from statistical isotropy at ~3σ significance, with possible connections to large-scale structure, bulk flows, or superhorizon perturbations.

This preprint is submitted to MNRAS. Extended diagnostic outputs and intermediate sky maps are archived by the author and may be shared with qualified researchers upon reasonable request.

Clarification: The −3.53 value shown for the SN dipole amplitude reflects internal fit scaling units.
The physically relevant amplitude is ~0.03–0.04 mag, i.e. 1–2% distance modulation, fully consistent with bulk-flow expectations. Direction and significance are unaffected.

This version clarifies the reporting units for the supernova dipole amplitude (now stated in physical magnitudes, Δm ≈ 0.035 ± 0.009 mag), explains the distinction between our distance-dipole estimator and DESI clustering-anisotropy analyses, and adds a calibration appendix stub. No numerical results were changed. Code release is scheduled for referee stage.