The lack of information about the nature of dark energy and dark matter allow us to widely speculate about the physical mechanisms beyond such mysterious components. If dark energy is assumed to be a dynamical entity, nothing prevents it to interact with dark matter at large scales. Cosmological models where a coupling in the dark sector plays an important role are interesting from both theoretical and observational perspectives. Such interactions can in fact provide a solution to the coincidence problem, as well as better accomodate the observational data. But which is the most general cosmological model of interacting dark energy? In this talk I will show how the most general coupling between dark energy and dark matter can be obtained following general considerations about interacting cosmological fluids. From this analysis the phenomenological arena over which theories of interacting dark energy can be defined will be greatly expanded. I will provide examples and discussions on the properties and possible applications of new theories which can be constructed from such approach. Furthermore I will discuss how coupled quintessence models derived from different Lagrangian formulations naturally belong to this new class of interactions in the dark sector.

IPhT-CEA