Exploring non-cold dark matter in a scenario of dynamical dark energy with DESI DR2 data

Abstract: Recent observations of DESI hint that dark matter (DM) may not be cold but have a non-zero equation of state (EoS) parameter, and that dark energy (DE) may not be a cosmological constant. In this work, we explore the possibility of a non-zero DM EoS parameter within the framework of dynamical DE. We perform analysis by using the latest baryon acoustic oscillation (BAO) data from DESI DR2, the cosmic microwave background (CMB) data from Planck, and the type Ia supernova (SN) data from DESY5 and PantheonPlus. When using the combination of CMB, BAO, and SN data, our results indicate a preference for a non-zero DM EoS parameter at the $2.8\sigma$ and $3.3\sigma$ level within the content of a constant DE EoS. In contrast, for a time-evolving DE EoS parameterized by $w_0$ and $w_a$, this preference decreases to $0.8\sigma$ and $1.1\sigma$. Furthermore, allowing a non-zero DM EoS yields best-fit values of $w_0$ and $w_a$ that exhibit smaller deviations from the $\Lambda$CDM expectations, and Bayesian evidence analysis shows a comparable preference for this model relative to $\Lambda$CDM. The overall results of this work indicate that a non-zero DM EoS parameter warrants further exploration and investigation.