Campus, Varian 355
To date, all evidence for Cold Dark Matter (CDM) is still purely gravitational and thus the CDM paradigm remains to be thoroughly tested. In calculations of the Cosmic Microwave Background (CMB) anisotropies, CDM is usually modelled as pressureless perfect fluid. In the present work, we test the CDM paradigm by replacing the pressureless perfect fluid description by an imperfect fluid called Generalised Dark Matter (GDM). The standard CDM is nested in this new model which possesses more degrees of freedom and parameters. The GDM is indeed able to model natural deviations from a pressurless perfect fluid, with non-zero equation of state, sound speed, and viscosity.
Using the Planck CMB data (and various other datasets), we present here the best constraints on the GDM model to date. This includes cases where all its parameters are allowed to vary independently in time in a non-parametric way, and cases where we model nonlinear effects using a GDM halo model, which allowed us to robustly include datasets from galaxy surveys to significantly tighten the constraints on GDM parameters.
(constraints: 1601.05097, 1802.09541, 1905.02739, model: 1605.00649)