Cosmological Constraints on Interacting Dark Matter with SPT-3G D1

Abstract

Models of the dark sector in which the dark matter participates in nontrivial interactions can create detectable signatures in cosmological observables, providing non-terrestrial means of probing the nature of dark matter. In this work, we test dark matter-baryon scattering, dark matter-dark radiation interactions, and dark matter annihilation using measurements of the CMB and BAO. We leverage the latest SPT-3G D1 CMB measurements of the primary anisotropies, alongside the D1 MUSE lensing data, to set up-to-date bounds on these models. From the combination of Planck, ACT DR6, and SPT-3G D1 data, we constrain the velocity-independent dark matter-baryon scattering cross-section to $σ_\mathrm{DM-b} < 4.6\times10^{-26}~\mathrm{cm^2}$, the dark matter-dark radiation momentum transfer rate to $Γ_\mathrm{0,nadm}<5.2\times10^{-8}\,\text{Mpc}^{-1}$, and the effective dark matter annihilation parameter, quantifying the fractional thermally averaged cross-section, to $p_\mathrm{ann}<3.7\times10^{-28}~\mathrm{cm^3/s/GeV}$, all at the 95% confidence level. The improved sensitivity to the first two models is in particular driven by the precision measurements of CMB lensing at small scales provided by SPT-3G D1 MUSE lensing data. For annihilating dark matter, due to the degeneracy of the effect with the optical depth to reionization, we observe a non-trivial relationship between the upper bound on $p_\mathrm{ann}$ and the large-scale polarization information. When combining CMB data with the latest measurements from the Dark Energy Spectroscopic Instrument (DESI), upper bounds on extended model parameters can appear to tighten as the model space attempts to accommodate the known discrepancy between these data. Future CMB and BAO measurements will provide better clarity on reconciling this discrepancy and enhance our ability to test dark matter interactions.