Phantom Scalar Field Research Articles

Dark sector impact on gravitational collapse of an electrically charged scalar field

Dark matter and dark energy are dominating components of the Universe. Their presence affects the course and results of processes, which are driven by the gravitational interaction. The objective of the paper was to examine the influence of the dark sector on the gravitational collapse of an electrically charged scalar field. A phantom scalar field was used as a model of dark energy in the system. Dark matter was modeled by a complex scalar field with a quartic potential, charged under a U(1)-gauge field. The dark components were coupled to the electrically charged scalar field via the exponential coupling and the gauge field-Maxwell field kinetic mixing, respectively. Complete non-linear simulations of the investigated process were performed. They were conducted from regular initial data to the end state, which was the matter dispersal or a singularity formation in a spacetime. During the collapse in the presence of dark energy dynamical wormholes and naked singularities were formed in emerging spacetimes. The wormhole throats were stabilized by the violation of the null energy condition, which occurred due to a significant increase of a value of the phantom scalar field function in its vicinity. The square of mass parameter of the dark matter scalar field potential controlled the formation of a Cauchy horizon or wormhole throats in the spacetime. The joint impact of dark energy and dark matter on the examined process indicated that the former decides what type of an object forms, while the latter controls the amount of time needed for the object to form. Additionally, the dark sector suppresses the natural tendency of an electrically charged scalar field to form a dynamical Reissner-Nordstr\"om spacetime during the gravitational collapse.

Localization and mass spectra of bulk bosonic fields on de Sitter thick branes

A thick de Sitter brane constructed by a canonical or phantom scalar field and localization mass spectra of the bulk scalar and vector fields on the de Sitter brane is investigated. It is found that the scalar and vector zero modes are always localized on the de Sitter brane. For the de Sitter brane generated by a canonical scalar field, the spectrum of the scalar (vector) KK modes consists of one or two bound modes (one bound mode) and a set of continuous modes. However, for the de Sitter brane generated by a phantom scalar field, the spectrum of the scalar (vector) KK modes consists of two (one) or more bound KK modes as well as a set of continuous modes. The continuous spectrum on both branes starts with a same value for the scalar (vector) KK modes.

Stationary cylindrically symmetric spacetimes with a massless scalar field and a nonpositive cosmological constant

The general stationary cylindrically symmetric solution of Einstein-massless scalar field system with a nonpositive cosmological constant is presented. It is shown that the general solution is characterized by four integration constants. Two of these essential parameters have a local meaning and characterize the gravitational field strength. The other two have a topological origin, as they define an improper coordinate transformation that provides the stationary solution from the static one. The Petrov scheme is considered to explore the effects of the scalar field on the algebraic classification of the solutions. In general, these spacetimes are of type I. However, the presence of the scalar field allows us to find a nonvacuum type O solution and a wider family of type D spacetimes, in comparison with the vacuum case. The mass and angular momentum of the solution are computed using the Regge-Teitelboim method in the case of a negative cosmological constant. In absence of a cosmological constant, the curvature singularities in the vacuum solutions can be removed by including a phantom scalar field, yielding nontrivial locally homogeneous spacetimes. These spacetimes are of particular interest, as they have all their curvature invariants constant.

Dilatonic dyon black hole solutions

Dilatonic black hole dyon solutions with an arbitrary dilatonic coupling constant and canonical sign for the scalar field kynetic term are considered. These solutions are defined up to solutions of two master equations for moduli functions. For the solutions are extended to = ±1, where corresponds to a ghost (phantom) scalar field. Some physical parameters of the solutions: gravitational mass, scalar charge, Hawking temperature, black hole area entropy and parametrized post-Newtonian (PPN) parameters β and γ are obtained. It is shown that PPN parameters do not depend on scalar field coupling λ and ϵ. Two groups of bounds on gravitational mass and scalar charge (for a fixed and arbitrary extremality parameter ) are found by using a certain conjecture on parameters of solutions when . These bounds are verified numerically for certain examples. Using the product we are led to the well-known lower bound on mass which was obtained earlier by Gibbons, Kastor, London, Townsend and Traschen by using spinor techniques.

Quantum cosmology with scalar fields: Self-adjointness and cosmological scenarios

We discuss the issue of unitarity in particular quantum cosmological models with scalar field. The time variable is recovered, in this context, by using the Schutz's formalism for a radiative fluid. Two cases are considered: a phantom scalar field and an ordinary scalar field. For the first case, it is shown that the evolution is unitary provided a convenient factor ordering and inner product measure are chosen; the same happens for the ordinary scalar field, except for some special cases for which the Hamiltonian is not self-adjoint but admits a self-adjoint extension. In all cases, even for those cases not exhibiting unitary evolution, the formal computation of the expectation value of the scale factor indicates a non-singular bounce. The importance of the unitary evolution in quantum cosmology is briefly discussed.

Unified universe history through phantom extended Chaplygin gas

The universe evolution from inflation to late-time acceleration is investigated in a unified way, using a two-component fluid constituted from extended Chaplygin gas alongside a phantom scalar field. We extract solutions for the various cosmological eras, focusing on the behavior of the scale factor, the various density parameters and the equation-of-state parameter. Furthermore, we extract and discuss bouncing solutions. Finally, we examine the perturbations of the model, ensuring their stability and extracting the predictions for the tensor-to-scalar ratio.

Magnetic wormholes and black universes with invisible ghosts

We construct explicit examples of globally regular static, spherically symmetric solutions in general relativity with scalar and electromagnetic fields describing traversable wormholes with flat and AdS asymptotics and regular black holes, in particular, black universes. (A black universe is a regular black hole with an expanding, asymptotically isotropic space-time beyond the horizon.) The existence of such objects requires invoking scalars with negative kinetic energy ("phantoms", or "ghosts"), which are not observed under usual physical conditions. To account for that, the so-called "trapped ghosts" were previously introduced, i.e., scalars whose kinetic energy is only negative in a restricted strong-field region of space-time and positive outside it. This approach leads to certain problems, including instability (as is illustrated here by derivation of an effective potential for spherical pertubations of such systems). In this paper, we use for model construction what we call "invisible ghosts", i.e., phantom scalar fields sufficiently rapidly decaying in the weak-field region. The resulting configurations contain different numbers of Killing horizons, from zero to four.

Dynamics of Mixed Dark Energy Domination in Teleparallel Gravity and Phase-Space Analysis

We consider a novel dark energy model to investigate whether it will provide an expanding universe phase. Here we propose a mixed dark energy domination which is constituted by tachyon, quintessence, and phantom scalar fields nonminimally coupled to gravity, in the absence of background dark matter and baryonic matter, in the framework of teleparallel gravity. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions implying the acceleration phase of universe.

Rotating Ellis wormholes in four dimensions

We present rotating wormhole solutions in General Relativity, which are supported by a phantom scalar field. These solutions evolve from the static Ellis wormhole, when the throat is set into rotation. As the rotational velocity increases, the throat deforms until at a maximal value of the rotational velocity, an extremal Kerr solution is encountered. The rotating wormholes attain a finite mass and quadrupole moment. They exhibit ergospheres and possess bound orbits.

Modified f(R,T) gravity theory and scalar field cosmology

In this paper, we explore the behaviors of scalar field in modified f(R,T) gravity theory within the framework of a flat Friedmann-Robertson-Walker cosmological model. The universe is assumed to be filled with two non-interacting matter sources, scalar field (normal or phantom) with scalar potential and matter contribution due to f(R,T) action. We first explore a model where the potential is a constant, and the universe evolves as a de Sitter type. This model is compatible with phantom scalar field only which gives fine tuning with the recent observations. The model exhibits a wide variety of early time physical phenomena that eventually behaves like a cosmological constant at late times. The model shows transition from decelerated to accelerated expansion of the universe. We also explore a model where the scalar field potential and the scale factor evolve exponentially as a scalar field. This model is compatible with normal scalar field only and describes transition from inflationary to the decelerated phase at early times and quintessence to phantom phase at late times. We constraint our results with the recent observational data and find that some values of parameters are consistent with SNe Ia and H(z)+SNe Ia data to describe accelerated expansion only whereas some one give decelerated and accelerated expansions with H(z), WMAP7 and WMAP7+BAO+H(z) observational data.

Wave dynamics of a phantom field in a traversable wormhole spacetime

In this paper, we study the wave dynamics of a phantom field in traversable wormholes. We compute the radial equation of the phantom field in the background of traversable wormholes. The majority of a phantom scalar field is shown to be distributed near the throat. The more massive the phantom field is, the denser it is near the throat.

Exact Inflationary Solutions Inspired by the Emergent Universe Scenario

We present new classes of exact inflationary solutions for a two-component chiral cosmological model with phantom and canonical scalar fields. These solutions are obtained by use of the scale factor in the form corresponding to that exploited in the emergent universe scenario. We outline in detail the method of deriving exact solutions and discuss the potential and kinetic interaction for the model.

Dynamical system analysis for a phantom model

The paper deals with a dynamical system analysis related to phantom cosmological model . Here gravity is coupled to phantom scalar field having scalar coupling function and a potential. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables and assuming some suitable form of the potential function. Finally, critical points are evaluated, their nature have been analyzed and corresponding cosmological scenario has been discussed.

Selection rules for the Wheeler-DeWitt equation in quantum cosmology

Selection of physically meaningful solutions of the Wheeler-DeWitt equation for the wavefunction in quantum cosmology, can be attained by a reduction of the theory to the sector of true physical degrees of freedom and their canonical quantization. The resulting physical wavefunction unitarily evolving in the time variable introduced within this reduction can then be raised to the level of the cosmological wavefunction in superspace of 3-metrics. We apply this technique in several simple minisuperspace models and discuss both at classical and quantum level physical reduction in {\em extrinsic} time -- the time variable determined in terms of extrinsic curvature. Only this extrinsic time gauge can be consistently used in vicinity of turning points and bounces where the scale factor reaches extremum. Since the 3-metric scale factor is canonically dual to extrinsic time variable, the transition from the physical wavefunction to the wavefunction in superspace represents a kind of the generalized Fourier transform. This transformation selects square integrable solutions of the Wheeler-DeWitt equation, which guarantee Hermiticity of canonical operators of the Dirac quantization scheme. Semiclassically this means that wavefunctions are represented by oscillating waves in classically allowed domains of superspace and exponentially fall off in classically forbidden (underbarrier) regions. This is explicitly demonstrated in flat FRW model with a scalar field having a constant negative potential and for the case of phantom scalar field with a positive potential. The FRW model of a scalar field with a vanishing potential does not lead to selection rules for solutions of the Wheeler-DeWitt equation, but this does not violate Hermiticity properties, because all these solutions are anyway of plane wave type and describe cosmological dynamics without turning points and bounces.

Viscous dark energy and phantom field in an anisotropic universe

In this paper we have investigated the general form of viscous and non-viscous dark energy equation of state (EoS) parameter in the scope of anisotropic Bianchi type I space-time. We show that the presence of bulk viscosity causes transition of ω de from quintessence to phantom but the phantom state is an unstable state (as expected) and EoS of DE tends to −1 at late time. Then we show this phantomic description of the viscous dark energy and reconstruct the potential of the phantom scalar field. It is found that bulk viscosity pushes the universe to a darker region. We have also shown that at late time q∼−Ω de .

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

Past analyses of the equation of state (EoS) of the Dark Energy (DE) were not incompatible with 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 did not completely disappear from the data collected from the Planck satellite mission. In it the EoS analysis may still be interpreted as suggesting w<-1, and so a mildly evolving DE cannot be discarded. In our opinion the usual ansatzs 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.

An Emergent Universe with Dark Sector Fields in a Chiral Cosmological Model

We consider the emergent universe scenario supported by a chiral cosmological model with two interacting dark sector fields: phantom and canonical. We investigate the general properties of the evolution of the kinetic and potential energies as well as the development of the equation of state with time. We present three models based on asymptotic solutions and investigate the phantom part of the potential and chiral metric components. The exact solution corresponding to a global emergent universe scenario, starting from the infinite past and evolving to the infinite future, has been obtained for the first time for a chiral cosmological model. The behavior of the chiral metric components responsible for the kinetic interaction between the phantom and canonical scalar fields has been analyzed as well.

Quintessence versus phantom dark energy: the arbitrating power of current and future observations

We analyze the possibility to distinguish between quintessence and phantom scalar field models of dark energy usingobservations of luminosity distance moduli of SNe Ia, CMB anisotropies and polarization, matter density perturbations andbaryon acoustic oscillations. Among the present observations only Planck data on CMB anisotropy and SDSS DR9 data on baryon acoustic oscillations may be able to decide between quintessence or phantom scalar field models, however for each model a set of best-fit parameters exists, which matches all data with similar goodness of fit. We compare the relative differences of best-fit model predictions with observational uncertainties for each type of data and we show that the accuracy of SNe Ia luminosity distance data is far from the one necessary to distinguish these types of dark energy models, while the CMB data (WMAP, ACT, SPT and especially Planck) are close to being able to reliably distinguish them. Also an improvement of the large-scale structure data (future releases of SDSS BOSS and e.g. Euclid or BigBOSS) will enable us to surely decide between quintessence and phantom dark energy.

Thick brane isotropization in a generalized 5D anisotropic standing wave braneworld model

We study a smooth cosmological solution within a generalized 5D standing wave braneworld modeled by gravity and a phantom scalar field. In this model the 3-brane is anisotropically warped along its spatial dimensions and contains a novel time-dependent scale factor that multiplies the anisotropic spatial interval of the 5D metric, a fact that allows us to study cosmological effects. By explicitly solving the bulk field equations we found a natural mechanism which isotropizes the braneworld for a wide class of natural initial conditions. We are able to give a physical interpretation of the anisotropic dissipation: as the anisotropic energy of the 3-brane rapidly leaks into the bulk through the nontrivial components of the nonlocal Weyl tensor projected to the brane, the bulk becomes less isotropic. At the same time, under the action of the 4D cosmological constant, the anisotropic braneworld super-exponentially isotropizes by itself, rendering a 3-brane with de Sitter symmetry embedded in a 5D de Sitter space-time, while the phantom scalar field exponentially vanishes.

Gravitational lensing by phantom black holes

In some models dark energy is described by phantom scalar fields (scalar fields with "wrong" sign of the kinetic term in the lagrangian). In the current paper we study the effect of phantom scalar field and/or phantom electromagnetic field on gravitational lensing by black holes in the strong deflection regime. The black-hole solutions that we have studied have been obtained in the frame of the Einstein-(anti-)Maxwell-(anti-)dilaton theory. The obtained results show considerable effect of the phantom scalar and electromagnetic fields on the angular position, brightness and separation of the relativistic images.