We investigate the validity of the thermodynamical properties of the universe in a new parametric model of dark energy with the equation of state w = w 0 +w 1 ·z(1+z)/(1+z 2 ). In the spatially homogeneous and isotropic universe, assuming that the temperature and entropy in cosmology is as in a black hole, we examine the thermodynamical properties of the universe bounded by the apparent horizon and the event horizon respectively. By analysis, we find that the first and the second laws of thermodynamics are valid inside the apparent horizon, while they break down inside the event horizon. Keywords: Dark energy; the thermodynamical properties; apparent horizon; event horizon. PACS Nos.: 98.80.-k, 98.80.Cq 885 Mod. Phys. Lett. A 2011.26:885-892. Downloaded from www.worldscientific.com by UNIVERSITY OF CALIFORNIA @ SAN DIEGO on 02/03/15. For personal use only. 886 L. Xing et al.

We consider a model that charged static spherically-symmetric black hole is surrounded by dark fluid with nonlinear equation of state p d = −B/ρ d . We find that the energy density of the dark fluid can be characterized by two parameters. The derivation of metric solution, as well as the calculation of black hole thermodynamical quantities as functions of horizon radius, are performed. Specially, in D-dimensional Einstein gravity and Gauss-Bonnet gravity cases, we plot the metric functions and corresponding thermodynamical quantities, such as mass, Hawking temperature and heat capacity, by varying the values of spacetime dimensions and dark fluid parameters. The effects of the dark fluid parameters on black hole solutions as well as on thermodynamical stability of black holes are discussed. Number(s): 04.20.Cv, 04.50.Gh, 95.35.+d PACS

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