Title: Interactions and Instabilities in Cosmology's Dark Sector


Theories possessing a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the universe may exhibit an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, determined by the local dark matter density. I will discuss a generic instability in such situations, arising when If the coupling strength becomes much larger than gravitational. I will demonstrate how this instability occurs, and illustrate it by considering specific coupled CDM and Mass Varying Neutrino (MaVaN) models of dark energy.