Thermodynamics of dark energy

Thermodynamic properties of dark energy are discussed assuming that dark energy is described in terms of a selfinteracting complex scalar. We first show that, under certain assumptions, selfinteracting complex scalar field theories are equivalent to purely kinetic k-essence models. Then we analazie the themal properties of k-essence and in particular we show that dark-energy in the phantom regime does not necesserely yield negative entropy. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim.