Institut de recherche sur les lois fondamentales de l'Univers

Modern cosmology faces with an intriguing problem: it seems that 70% of the energy content of the Universe, in the standard scenario, is an unknown, almost homogeneously distributed, non interacting form of repulsive energy, called Dark Energy. After a short introduction to the standard model of cosmology and to the observational evidences for the Dark Energy component, I will review the various scenarii introduced to explain these observations, including the cosmological constant, new non-standard cosmological fluids (quintessence), modification of gravity and averaged cosmologies, with a particular emphasis on the degeneracies between the models and the possible ways to distinguish between them at the observational level.