Cosmic microwave background and large scale structure limits on the interaction between dark matter and baryons
Xuelei Chen, Steen Hannestad, Robert J. Scherrer
TL;DR
The paper investigates whether dark matter–baryon scattering with cross section $\sigma$ can imprint observable signatures on the CMB and LSS via momentum transfer. It develops a perturbation framework in the synchronous gauge, incorporates primordial helium with a fraction $Y$, and uses a modified version of CMBFAST to compute the resulting spectra. The results show that current CMB data place stringent upper limits on $\sigma$—comparable to or stronger than disk-heating constraints, especially for $m_c \lesssim 1$ GeV—with LSS data further tightening these bounds and ruling out Spergel-Steinhardt-like cross sections for $m_c > 1$ GeV. Together, these findings constrain strongly interacting dark matter scenarios and demonstrate the power of combining CMB and LSS observations to probe DM–baryon momentum-transfer interactions, with implications for SIMP-like models.
Abstract
We study the effect on the cosmic microwave background (CMB) anisotropy and large scale structure (LSS) power spectrum of a scattering interaction between cold dark matter and baryons. This scattering alters the CMB anisotropy and LSS spectrum through momentum transfer between the cold dark matter particles and the baryons. We find that current CMB observations can put an upper limit on the scattering cross section which is comparable with or slightly stronger than previous disk heating constraints at masses greater than 1 GeV, and much stronger at smaller masses. When large-scale structure constraints are added to the CMB limits, our constraint is more stringent than this previous limit at all masses. In particular, a dark matter-baryon scattering cross section comparable to the ``Spergel-Steinhardt'' cross section is ruled out for dark matter mass greater than 1 GeV.