Stepped Partially Acoustic Dark Matter: Likelihood Analysis and Cosmological Tensions

Understand

We generalize the recently proposed Stepped Partially Acoustic Dark Matter (SPartAcous) model by including additional massless degrees of freedom in the dark radiation sector.

• We fit SPartAcous and its generalization against cosmological precision data from the cosmic microwave background, baryon acoustic oscillations, large-scale structure, supernovae type Ia, and Cepheid variables.
• We find that SPartAcous significantly reduces the $H_0$ tension but does not provide any meaningful improvement of the $S_8$ tension, while the generalized model succeeds in addressing both tensions, and provides a better fit than $\Lambda\mathrm{CDM}$ and other dark sector models proposed to address the same tensions.
• In the generalized model, $H_0$ can be raised to $71.4~\mathrm{km/s/Mpc}$ (the 95% upper limit) if the fitted data does not include the direct measurement from the SH0ES collaboration, and to $73.7~\mathrm{km/s/Mpc}$ (95% upper limit) if it does.