Revisiting self-interacting dark matter with DESI DR2 baryon acoustic oscillation observations
We revisit self-interacting dark matter (SIDM), originally proposed to resolve small-scale CDM problems and drive late-time cosmic acceleration. Using latest DESI BAO, Pantheon+/DESY5 type Ia supernova, and cosmic chronometer Hubble data, we constrain three representative SIDM scenarios including creation and annihilation. We focus on the annihilation of dark matter particles in model SIDM1; our findings indicate the effective annihilation cross section is $\log_{10}(κC_1)=-4.32$ (with an upper limit of $\log_{10}(κC_1)=-3.90$). For the SIDM2 model, the SIDM fluid behaves similarly to a dark energy component with a mildly dynamical equation of state ($w_{\rm{SIDM}}=-0.82 \pm 0.04$). We also quantitatively discuss the dark matter self-interactions in a more general SIDM model (SIDM3), which reveals a strong correlation between the annihilation cross section and equation of state of dark matter. For the three SIDM models, the measured Hubble constant agrees with that derived from the recent Planck 2018 results; both are inconsistent with the results of the SH0ES collaboration, who report a significantly higher $H_0$ value. The Bayesian evidence indicates that SIDM2 and SIDM3 are more supported by the available observational data than the concordance standard $Λ$CDM. Furthermore, the cosmological constraints on the effective annihilation parameter can be translated into bounds on the velocity-averaged annihilation cross section and the self-interaction cross section per unit mass. While low-redshift data alone imply a relatively large cross section, the inclusion of cosmic microwave background distance priors significantly tightens the constraint at cluster-scale velocities, highlighting the necessity of a velocity-dependent cross section to reconcile cosmological and astrophysical observations.