Non-comoving Cosmology

Understand

One of the fundamental assumptions of the standard $\Lambda$CDM cosmology is that, on large scales, all the matter-energy components of the Universe share a common rest frame.

• This seems natural for the visible sector, that has been in thermal contact and tightly coupled in the primeval Universe.
• The dark sector, on the other hand, does not have any non-gravitational interaction known to date and therefore, there is no a priori reason to impose that it is comoving with ordinary matter.
• In this work we explore the consequences of relaxing this assumption and study the cosmology of non-comoving fluids.