Phantom cosmologies

Abstract

The dynamics of a minimally coupled scalar field in the expanding universe is discussed with special reference to phantom cosmology. The evolution of the universe with a phantom field vis-a-vis a quintessence field is compared. Phantom cosmologies are found to have two special features i) occurrence of a singularity where the scale factor, the energy density and Ricci curvature scalar diverge to infinity. This singularity occurs at a finite timexs, depending on the value of w during cosmic evolution, ii) degeneracy in the determination of w(z m ) for a given transition redshift z m which seems to impart similar observational properties to corresponding phantom and quintessence models and makes both of them compatible with the cosmological observations. Although due to the uncertainties in the measurement of the Hubble constant H 0 , the Hubble dependent observational parameters yield only loose constraints over the range of w, the duality in the determination of w with respect to transition redshift may be used to constrain w. An observational test, based upon the observations of low redshift galactic clusters, is suggested to discriminate between the quintessence and phantom dark energy. PACS numbers: 98.80.Cq, 98.65. Dx,98.70.Vc

Variable G and ?: scalar-tensor versus RG-improved cosmology

“…There is also evidence for some consistency between the current cosmic age estimator data and phantom energies [27,29]. A discussion on whether this component of the universe may lead to a big rip [30,31] or not [32,33] is still open, even if the occurrence of a possible singularity in the next future has recently been discussed also when ρ Q > 0 and ρ Q + 3p Q > 0 [34].…”

Dark Energy

“…One can see [7,543,544,545,546,547] and references therein for more studies on the scalar field models from the aspect of observations. In addition, there are also some theories using vector fields to describe dark energy [284,548,549,550].…”

Accretion processes for general spherically symmetric compact objects

“…This discovery was a revolution in cosmology and the agent responsible for this effect was named dark energy. This energy has the strange property that produces repulsive gravitational effects and it violates the null and weak energy condition [5,6]. Surprisingly, observations suggests that around two-thirds of the total energy of the Universe belongs to the dark energy [1,2].…”