Constraining the non-gravitational scattering of baryons and dark matter with early cosmic structure formation

Abstract

ABSTRACT We derive new constraints on the non-gravitational baryon-dark matter scattering (BDMS) by evaluating the mass thresholds of dark matter (DM) haloes in which primordial gas can cool efficiently to form Population III (Pop III) stars, based on the timing of the observed 21 cm absorption signal. We focus on the BDMS model with interaction cross-section $\sigma =\sigma _{1}[v/(1\ \mathrm{km\, s^{-1}})]^{-4}$, where v is the relative velocity of the encounter. Our results rule out the region in parameter space with $\sigma _{1}\gtrsim 10^{-19}\, \mathrm{cm^{2}}$ and DM particle mass mχc2 ≲ 3 × 10−2 GeV, where the cosmic number density of Pop III hosts at redshift z ∼ 20 is at least three orders of magnitude smaller than in the standard Lambda cold DM (ΛCDM) case. In these BDMS models, the formation of Pop III stars is significantly suppressed for z ≳ 20, inconsistent with the timing of the observed global 21 cm absorption signal. For the fiducial BDMS model with mχc2 = 0.3 GeV and $\sigma _{1}=8\times 10^{-20}\, \mathrm{cm^{2}}$, capable of accommodating the measured absorption depth, the number density of Pop III hosts is reduced by a factor of 3−10 at z ∼ 15−20, when the 21 cm signal is imprinted, compared with the ΛCDM model. The confluence of future detailed cosmological simulations with improved 21 cm observations promises to probe the particle-physics nature of DM at the small-scale frontier of early structure formation.