ACT DR6 Leads to Stronger Evidence for Dynamical Dark Matter

Abstract: Dark matter is fundamental to the composition, structure, and evolution of the universe. Combining the ACT's cosmic microwave background, DESI's baryon acoustic oscillations with DESY5 type Ia supernova observations, we find a $3.4\,\sigma$ evidence for dynamical dark matter (DDM) with an equation of state, $\omega_{dm}(a)=\omega_{dm0}+\omega_{dma}(1-a)$. Independent of the Planck measurements, the ACT data confirms the linear relation $\omega_{dma}=-\omega_{dm0}$, inducing that the equation of state of dark matter is directly proportional to the scale factor $a$. Furthermore, the effects of DDM on the large-scale structure observables are thoroughly studied. Our findings are of great significance for understanding cosmic acceleration, structure growth, and the fate of the universe.