Phantom energy versus cosmological constant: Comparative results via analytical solutions of the Wheeler-DeWitt equation (original) (raw)
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Phantom dark energy and cosmological solutions without the Big Bang singularity
Physics Letters B - PHYS LETT B, 2010
The hypothesis is rapidly gaining popularity that the dark energy pervading our universe is extra-repulsive (-p>rho). The density of such a substance (usually called phantom energy) grows with the cosmological expansion and may become infinite in a finite time producing a Big Rip. In this Letter we analyze the late stages of the universe evolution and demonstrate that the presence of the phantom energy in the universe is not enough in itself to produce the Big Rip. This singularity occurrence requires the fulfillment of some additional, rather strong conditions. A more probable outcome of the cosmological evolution is the decay of the phantom field into `normal' matter. The second, more intriguing consequence of the presence of the phantom field is the possibility to introduce a cosmological scenario that does not contain a Big Bang. In the framework of this model the universe eternally expands, while its density and other physical parameters oscillate over a wide range, nev...
Exact solutions of the Wheeler–DeWitt equation with ordering term in a dark energy scenario
Physics of the Dark Universe, 2020
We investigate the quantum evolution of the universe in the presence of two types of dark energies. First, we consider the phantom class (ω < −1) which would be responsible for a superaccelerated cosmic expansion, and then we apply the procedure to an ordinary Λ > 0 vacuum (ω = −1). This is done by analytically solving the Wheeler-DeWitt equation with ordering term (WdW) in the cosmology of Friedmann-Robertson-Walker. In this paper, we find exact solutions in the scale factor a and the ordering parameter q. For q = 1 it is shown that the universe has a high probability of evolving from a big bang singularity. On the other hand, for q = 0 the solution indicates that an initial singularity is unlikely. Instead, the universe has maximal probability of starting with a finite well-defined size which we compute explicitly at primordial times. We also study the time evolution of the scale factor by means of the Hamilton-Jacobi equation and show that an ultimate big rip singularity emerges explicitly from our solutions. The phantom scenario thus predicts a dramatic end in which the universe would reach an infinite scale factor in a finite cosmological time as pointed by Caldwell et al. in a classical setup [1]. Finally, we solve the WdW equation with ordinary constant dark energy and show that in this case the universe does not rip apart in a finite era.
Cosmological Perturbations in Phantom Dark Energy Models
Universe
The ΛCDM paradigm, characterised by a constant equation of state w = −1 for dark energy, is the model that better fits observations. However, the same observations strongly support the possibility of a dark energy content where the corresponding equation of state is close to but slightly smaller than −1. In this regard, we focus on three different models where the dark energy content is described by a perfect fluid with an equation of state w −1 which can evolve or not. The three proposals show very similar behaviour at present, while the asymptotic evolution of each model drives the Universe to different abrupt events known as (i) Big Rip; (ii) Little Rip (LR); and (iii) Little Sibling of the Big Rip. With the aim of comparing these models and finding possible imprints in their predicted matter distribution, we compute the matter power spectrum and the growth rate f σ 8. We conclude that the model which induces a LR seems to be favoured by observations.
Cosmological perturbations in an effective and genuinely phantom dark energy Universe
Physics of the Dark Universe, 2017
We carry out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the Universe. These three setups are described classically by perfect fluids with a phantom nature and represent deviations from the most widely accepted ΛCDM model. In addition, each of the models under study induce different future singularities or abrupt events known as (i) Big Rip, (ii) Little Rip and (iii) Little Sibling of the Big Rip. Only the first one is regarded as a true singularity since it occurs at a finite cosmic time. For this reason, we refer to the others as abrupt events. With the aim to find possible footprints of this scenario in the Universe matter distribution, we not only obtain the evolution of the cosmological scalar perturbations but also calculate the matter power spectrum for each model. We have carried the perturbations in the absence of any anisotropic stress and within a phenomenological approach for the speed of sound. We constrain observationally these models using several measurements of the growth rate function, more precisely f σ8, and compare our results with the observational ones.
Fate of the phantom dark energy universe in semiclassical gravity. II. Scalar phantom fields
Physical Review D, 2012
Quantum corrections coming from massless fields conformally coupled with gravity are studied, in order to see if they can lead to avoidance of the annoying Big Rip singularity which shows up in a flat Friedmann-Robertson-Walker universe filled with dark energy and modeled by a scalar phantom field. The dynamics of the model are discussed for all values of the two parameters, named α > 0 and β < 0, corresponding to the regularization process. The new results are compared with the ones obtained in [1] previously, where dark energy was modeled by means of a phantom fluid with equation of state P = ωρ, with ω < −1.
Energy States of Universe and New Phantom Energy
2009
Energy states of the universe is obtained when the scale factor is defined as a=At^n, and n varies as -1<=n<=1,with the aid of the wavefunction which was constructed in, Mahgoub Salih, A Canonical Quantization formalism of curvature squared action. we found new properties of early Phantom energy, which it`s energy density increases with time while w=-1/3 .
A gracious exit from the matter-dominated phase in a quantum cosmic phantom model
Physics Letters B, 2014
The most recent observational constraints coming from Planck, when combined with other cosmological data, provide evidence for a phantom scenario. In this work we consider a quantum cosmic phantom model where both the matter particles and scalar field are associated with quantum potentials which make the effective mass associated with the matter particles to vanish at the time of matter-radiation equality, resulting in a cosmic system where a matter dominance phase followed by an accelerating expansion is allowed.
International Journal of Modern Physics D, 2005
We present a general algorithm based on the concept of forminvariance which can be used for generating phantom cosmologies. It involves linear transformations between the kinetic energy and the potential of the scalar field, and transforms solutions of the Einstein-Klein-Gordon equations which preserve the weak energy condition into others which violate it, while keeping the energy density of the field positive. All known solutions representing phantom cosmologies are unified by this procedure. Using the general algorithm we obtain those solutions and show the relations between them. In addition, the scale factors of the product and seed solutions are related by a generalization of the well-known a → a −1 duality. * chimento@df.uba.ar * * wtplasar@lg.ehu.es