Amjad Ashoorioon (IPM, Tehran)

Releasing the Cosmological Tensions

The standard cosmological model is in the midst of a stress test, thanks to the tension between supernovae-based measurements of the Hubble constant, H0, and inferences of its values from Cosmic Microwave Background (CMB) anisotropies. There is also disagreement in the value of matter density at 8Mpc/h, as implied by the CMB (when fit by the LambdaCDM model) and the value inferred from measurements of the amplitude of matter density fluctuations in the late-time Universe. The former is known as the H0 tension, and the latter, as sigma_8 tension. In the first part of my talk, I will try to address the H0 tension in a cascading scenario where multiple fields cooperatively contribute to the dark energy component in bursts throughout cosmic time due to distinct initial conditions and couplings. In the second part of my talk, I consider varying forms of viscous dark matter and try to address the aforementioned tensions. In particular, assuming the dark matter viscosity depends on the Hubble parameter, dark matter density, or both, one can improve the statistics. Although the models tend to aggravate the Hubble tension a bit, they tend to reduce the sigma_8 tension, even in comparison with the constant viscosity case.