Holographic Dark Energy and Present Cosmic Acceleration

We review the notion of holographic dark energy and assess its significance in the light of the well documented cosmic acceleration at the present time. We next propose a model of holographic dark energy in which the infrared cutoff is set by the Hubble scale. The model accounts for the aforesaid acceleration and, by construction, is free of the cosmic coincidence problem.Comment: 6 pages. To appear in the Proceedings of the XXVIII Spanish Relativity Meeting. Key words: Cosmology, Holography, Late accelerated expansion, Dark energ

Relic gravitational waves and the generalized second law

The generalized second law of gravitational thermodynamics is applied to the present era of accelerated expansion of the Universe. In spite of the fact that the entropy of matter and relic gravitational waves inside the event horizon diminish, the mentioned law is fulfilled provided that the expression for the entropy density of the gravitational waves satisfies a certain condition.Comment: 10 pages, 1 postscript figure, uses revtex4, PACS numbers: 04.30.-w, 98.80.-k published in the Physical Review

Statefinder parameters for interacting dark energy

We argue that the recently introduced "statefinder parameters" (Sahni et al., JETP Lett. 77, 201 (2003)), that include the third derivative of the cosmic scale factor, are useful tools to characterize interacting quitessence models. We specify the statefinder parameters for two classes of models that solve, or at least alleviate, the coincidence problem.Comment: 11 pages, two encapsulated eps figures, key words: cosmology, accelerated expansion, statefinder parameter