Cosmological Dynamics of Scalar Field with Non-Minimal Kinetic Term

2018

Particles

Abstract:We review nonsingular static, spherically symmetric solutions of general relativity with minimally coupled scalar fields. Considered are wormholes and regular black holes (BHs) without a center, including black universes (BHs with expanding cosmology beyond the horizon). Such configurations require a "ghost" field with negative kinetic energy K. Ghosts can be invisible under usual conditions if K < 0 only in strong-field region ("trapped ghost"), or they rapidly decay at large radii. Before discussing particular examples, some general results are presented, such as the necessity of anisotropic matter for asymptotically flat or AdS wormholes, no-hair and global structure theorems for BHs with scalar fields. The stability properties of scalar wormholes and regular BHs under spherical perturbations are discussed. It is stressed that the effective potential V eff for perturbations has universal shapes near generic wormhole throats (a positive pole regularizable by a Darboux transformation) and near transition surfaces from canonical to ghost scalar field behavior (a negative pole at which the perturbation finiteness requirement plays a stabilizing role). Positive poles of V eff emerging at "long throats" (with the radius r ≈ r 0 + const · x 2n , n > 1, x = 0 is the throat) may be regularized by repeated Darboux transformations for some values of n.

Section: Resultsmentioning

confidence: 86%

Scalar Fields as Sources for Wormholes and Regular Black Holes

2018

Particles

“…If the matrix h ab is not positive-or negative-definite, some solutions due to (8) can be wormhole while others correspond to a canonical scalar and have a Fisher central singularity [13], but there are no solutions of trapped-ghost character.…”

Section: Scalar Fields With a Variable Kinetic Termmentioning

confidence: 99%

“…In this sense it can be said that the ghost is trapped. A possible transition between h > 0 and h < 0 in cosmology was considered in [8].…”

Section: Introductionmentioning

confidence: 99%

Trapped ghosts: a new class of wormholes

Sushkov

2010

Class. Quantum Grav.

We construct examples of static, spherically symmetric wormhole solutions in general relativity with a minimally coupled scalar field φ whose kinetic energy is negative in a restricted region of space near the throat (of arbitrary size) and positive far from it. Thus in such configurations a "ghost" is trapped in the strong-field region, which may in principle explain why no ghosts are observed under usual conditions. Some properties of general wormhole models with the φ field are revealed: it is shown that (i) trapped-ghost wormholes are only possible with nonzero potentials V (φ) ; (ii) in twice asymptotically flat wormholes, a nontrivial potential V (φ) has an alternate sign, and (iii) a twice asymptotically flat wormhole which is mirror-symmetric with respect to its throat has necessarily a zero Schwarzschild mass at both asymptotics.

“…In this sense it can be said that the ghost is trapped. A possible transition between h > 0 and h < 0 in cosmology was considered in [12]. Examples of such "trapped-ghost" wormholes have been obtained in [11].…”

Section: Introductionmentioning

confidence: 99%

Black universes with trapped ghosts

Donskoy²

2011

Gravit. Cosmol.

A black universe is a nonsingular black hole where, beyond the horizon, there is an expanding, asymptotically isotropic universe. Such models have been previously found as solutions of general relativity with a phantom scalar field as a source of gravity and, without phantoms, in a brane world of RS2 type. Here we construct examples of static, spherically symmetric black-universe solutions in general relativity with a minimally coupled scalar field φ whose kinetic energy is negative in a restricted strong-field region of space-time and positive outside it. Thus in such configurations a "ghost" is trapped in a small part of space, which may in principle explain why no ghosts are observed under usual conditions.