Entropic cosmology in a dissipative universe

Understand

The bulk viscosity of cosmological fluid and the creation of cold dark matter both result in the generation of irreversible entropy (related to dissipative processes) in a homogeneous and isotropic universe.

• To consider such effects, the general cosmological equations are reformulated, focusing on a spatially flat matter-dominated universe.
• A phenomenological entropic-force model is examined that includes constant terms as a function of the dissipation rate ranging from $\tilde{\mu} =0$, corresponding to a nondissipative $\Lambda$CDM (lambda cold dark matter) model, to $\tilde{\mu} =1$, corresponding to a fully-dissipative CCDM (creation of cold dark matter) model.
• A time evolution equation is derived for the matter density contrast, in order to characterize density perturbations in the present entropic-force model.