Speaker
Description
The ΛCDM model is currently our best description of the universe. However, the model does not
come without fault as discrepancies between theory and observation have emerged. Bulk viscosity
has been proposed as a possible extension to the ΛCDM model as to account for these mismatches.
We review two alternative scenarios for the study of relativistic dissipative hydrodynamics applied
to cosmological ?uids, namely the Eckart and Muller-Israel-Stewart (MIS) theories. Our objective
is to study the e?ects of bulk viscosity on the formation of large-scale structure via the evolution
of the metric potential and dark matter density perturbations. After reviewing the results from
standard cosmological perturbation theory, we compare the two competing theories for dissipa-
tive hydrodynamics. We investigate changes to the conservation equations as well as the Einstein
equations with the introduction of the bulk viscous pressure. We will then discuss the numerical
solutions found for the evolution of the metric potential as well as comment on the clustering prop-
erties of the dark matter density perturbations. We compare the results from the two competing
theories. We see that for the metric potential, the Eckart and MIS theories deviated from the
ΛCDM case. We comment on nature of current cosmic tensions in this context. Future work is
also discussed.
