Astro Lunch

Cosmic acceleration without dark energy or modified gravity

There is an abundance of models aiming to explain the accelerating expansion of the Universe, all of which share a seemingly-universal feature: they all require one or more new particles. In this talk I'll present and discuss a counterexample, in which cosmic acceleration arises purely due to interactions between dark matter and baryonic matter. The dark matter couples minimally to the spacetime metric, while baryons couple to an effective metric which depends on the dark matter density and four-velocity. I discuss the cosmology of this model at the level of the background and linear perturbations, and present some preliminary results comparing it to observations.