Recent measurements of galaxy distribution by the Dark Energy Spectroscopic Instrument (DESI) show a mild tension with the standard ΛCDM cosmological model, particularly when extrapolated to low redshifts from Cosmic Microwave Background (CMB) data. To address this discrepancy, a proposed solution posits that the inertial and gravitational masses of dark matter particles are not the same, implying a violation of the Equivalence Principle within the dark sector.

Analysis of CMB data, combined with Baryon Acoustic Oscillation (BAO) and Full Shape (FS) data from DESI DR1 (Data Release 1), or with BAO DR2 data alone, suggests the presence of a new long-range force in the dark sector. This force would have a strength of approximately β ~ 0.5% relative to gravity, at a statistical significance of ~2.5σ. A preliminary assessment combining FS DR1 and BAO DR2 data raises the evidence for these dark forces to ~3σ, though this figure ignores the not-yet-available cross-correlation between the two datasets.

This finding, if confirmed, would have profound implications for our understanding of dark matter and cosmology. The existence of a dark force and the violation of the Equivalence Principle in this sector could necessitate a revision of current cosmological models and open new avenues for physics beyond the Standard Model. Confirmation of these results through future analyses and the incorporation of cross-data correlations will be crucial to validate this hypothesis.