Cosmological vector modes and quantum gravity effects

Understand

In contrast to scalar and tensor modes, vector modes of linear perturbations around an expanding Friedmann--Robertson--Walker universe decay.

• This makes them largely irrelevant for late time cosmology, assuming that all modes started out at a similar magnitude at some early stage.
• By now, however, bouncing models are frequently considered which exhibit a collapsing phase.
• Before this phase reaches a minimum size and re-expands, vector modes grow.