Unified dark energy thermodynamics: varying w and the −1-crossing

Abstract

We investigate, in a unified and general way, the thermodynamic properties of dark energy with an arbitrary, varying equation-of-state parameter w(a). We find that all quantities are well defined and regular for every w(a), including at the −1-crossing, with the temperature being negative in the phantom regime (w(a) < −1) and positive in the quintessence one (w(a) > −1). The density and entropy are always positive while the chemical potential can be arbitrary. At the −1-crossing, both temperature and chemical potential are zero. The temperature negativity can only be interpreted in the quantum framework. The regular behavior of all quantities at the −1-crossing, leads to the conclusion that such a crossing does not correspond to a phase transition, but rather to a smooth cross-over. PACS numbers: 95.36.+x,

Lorentzian Wormholes Thermodynamics

“…The rigorous application of this method implies a wormhole horizon with negative temperature. This result, far from being lacking in a well defined physical meaning, can be interpreted in a natural way taking into account that, as it is well known (Gonzalez-Diaz & Siguenza, 2004;Saridakis et al, 2009), phantom energy also possesses negative temperature. We shall consider in the present study a general spherically symmetric and dynamic wormhole which, therefore, is described through metric (12) with a trapping horizon characterized by Θ − = 0 and 12 Θ + > 0.…”

“…Such a process would take place at both mouths producing, in the end of the day, outgoing radiation with negative temperature in both mouths. Nevertheless, it is well known that phantom energy, which is no more than a particular case of exotic matter, is characterized by a negative temperature (Gonzalez-Diaz & Siguenza, 2004;Saridakis et al, 2009). Thus, this result could be taken to be a consistency proof of the used method, as a negative radiation temperature simply express the feature to be expected that wormholes should emit a thermal radiation just of the same kind as that of the stuff supporting them, such as it also occurs with dynamical black holes with respect to usual matter and positive temperature.…”

“…The univocal characterization of dynamical wormholes implies not only that the area (and hence the entropy) of a dynamical wormhole always increases if there are no changes in the exoticity of the background (second law of wormhole thermodynamics), but also that the hole appears to thermally radiate. The results of the studies about phantom thermodynamics (Gonzalez-Diaz & Siguenza, 2004;Saridakis et al, 2009) allow us to provide this possible radiation with negative temperature with a well-defined physical meaning. Therefore, wormholes would emit radiation of the same kind as the matter which supports them (Martin-Moruno & Gonzalez-Diaz, 2009a;b), such as it occurs in the case of dynamical black hole evaporation with respect to ordinary matter.…”

“…As we will show, the key point in this study will not lie only in applying the formalism developed by Hayward (Hayward, 1994a;1996;1998;2004) to the wormhole spacetime, but in noticing that the results coming from the accretion method, (Babichev et al, 2004;Martin-Moruno et al, 2006) and Gonzalez-Diaz & Martin-Moruno, 2008), must be equivalent to those which will be obtained by the mentioned formalism; this fact will allow a univocal characterization of wormholes. Such a characterization, together with some results about phantom thermodynamics (Gonzalez-Diaz & Siguenza, 2004;Saridakis et al, 2009), which concluded that phantom energy would possess a negative temperature, would provide any possible Hawking-like radiation from wormholes with a well defined physical meaning. In this chapter, we will start by summarizing some previous concepts on the Morris and Thorne solution 2.1 and the Hayward formalism 2.1.…”

Generalized Second Law of Thermodynamics for Interacting Dark Energy in the DGP Braneworld

“…Here we assume as in ref [25] the temperature of the source inside the horizon is in equilibrium with the temperature associated with the horizon.…”