Cosmological constraints on non-cold dark matter from DESI DR2 measurements

Abstract

We investigate potential deviations from cold dark matter (CDM) using the latest Baryon Acoustic Oscillations (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI). Analyzing DESI data alone constrains the dark matter equation of state parameter $w_{\text{dm}}=-0.{042}_{-0.024}^{+0.047}$, revealing a mild preference for non-cold dark matter. This preference strengthens significantly in combined analyses, but reveals a striking tension in the inferred w_dm values from observations of different nature. The DESI+DESY5 combination yields $w_{\text{dm}}=-0.084\pm 0.035$, excluding CDM ($w_{\text{dm}}=0$) at 2.4σ significance. In contrast, Planck+DESI gives $w_{\text{dm}}=0.00077\pm 0.00038$, differing from concordance model at 2σ significance. The non-vanishing w_dm preference is particularly driven by low-redshift BAO measurements (z < 1.1), while higher redshift data remain consistent with ΛCDM. The preference for non-cold dark matter is more pronounced in DESI compared to the previous BAO surveys. All dataset combinations show significant improvement over the ΛCDM paradigm, providing preference for non-cold dark matter scenario except DESI+DESY3+DES-DOV case.