Thursday, July 18, 2013

1307.4748 (Spyros Basilakos et al.)

Effective equation of state for running vacuum: "mirage" quintessence
and phantom dark energy

Spyros Basilakos, Joan Sola
The analysis of the equation of state (EoS) of the Dark Energy (DE) has been persistently suggesting a phantom phase near our time. This has been the case in the years of WMAP observations, in combination with the remaining cosmological observables. Such situation, far from fading away from the latest accurate data on the cosmic microwave anisotropies collected from the PLANCK satellite mission, remains there unscathed. Despite it is claimed there is no much evidence for dynamical DE, the bare fact is that the EoS analysis still points to w<-1, and a mildly evolving DE cannot be discarded. In our opinion the usual ansatz made on the structure of the EoS for dynamical DE models (e.g. quintessence and the like) are too simplified. In this work we examine in detail some of these issues and suggest that a general class of models with a dynamical vacuum energy density could explain the persistent phantom anomaly, despite there is no trace of real phantom behavior in them. The spurious or "mirage" effect is caused by an attempt to describe them as if the DE would be caused by fundamental phantom scalar fields. Remarkably, the effective DE behavior can also appear as quintessence in transit to phantom, or vice versa.
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