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The thermodynamic properties of dark energy fluids described by an equation of state parameter $omega=p/rho$ are rediscussed in the context of FRW type geometries. Contrarily to previous claims, it is argued here that the phantom regime $omega<-1$ is not physically possible since that both the temperature and the entropy of every physical fluids must be always positive definite. This means that one cannot appeal to negative temperature in order to save the phantom dark energy hypothesis as has been recently done in the literature. Such a result remains true as long as the chemical potential is zero. However, if the phantom fluid is endowed with a non-null chemical potential, the phantom field hypothesis becomes thermodynamically consistent, that is, there are macroscopic equilibrium states with $T>0$ and $S>0$ in the course of the Universe expansion. Further, the negative value of the chemical potential resulting from the entropy constraint ($S>0$) suggests a bosonic massless nature to the phantom particles.
The accretion of a phantom fluid with non-zero chemical potential by black holes is discussed with basis on the Generalized Second Law of thermodynamics. For phantom fluids with positive temperature and negative chemical potential we demonstrate that
In [Schmidt PRD 80 123003 (2009)], the author suggested that dynamical dark energy (DDE) propagating on the phantom brane could mimick $Lambda$CDM. Schmidt went on to derive a phenomenological expression for $rho_{rm DE}$ which could achieve this. We
We study the time evolution of the test scalar and electromagnetic fields perturbations in configurations of phantom wormholes surrounded by dark energy with state parameter $omega< -1$. We observe obvious signals of echoes reflecting wormholes prope
We derive an analytical expression for the growth rate of matter density perturbations on the phantom brane (which is the normal branch of the Dvali-Gabadadze-Porrati model). This model is characterized by a phantomlike effective equation of state fo
A possible candidate for the present accelerated expansion of the Universe is phantom energy, which possesses an equation of state of the form $omegaequiv p/rho<-1$, consequently violating the null energy condition. As this is the fundamental ingredi