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Peter K. F. Kuhfittig

Publications and source records attributed to Peter K. F. Kuhfittig.

At least 73 records · Page 4Linked to original sources
arXiv2016

The stability of thin-shell wormholes with a phantom-like equation of state

This paper discusses the stability to linearized radial perturbations of spherically symmetric thin-shell wormholes with a "phantom-like" equation of state for the exotic matter at the throat: $P=ωσ$, $ω<0$, where $σ$ is the energy-density of the shell and $P$ the surface pressure. This equation is analogous to the generalized Chaplygin-gas equation of state used by E.F. Eiroa. The analysis, which differes from Eiroa's in its basic approach, is carried out for wormholes constructed from the following spacetimes: Schwarzschild, de Sitter and anti de Sitter, Reissner-Nordstrom, and regular charged black-hole spacetimes, as well as from black holes in dilaton and generalized dilaton-axion gravity.

gr-qc↗
arXiv2016

Stable wormholes on a noncommutative-geometry background admitting a one-parameter group of conformal motions

When Morris and Thorne first proposed the possible existence of traversable wormholes, they adopted the following strategy: maintain complete control over the geometry, thereby leaving open the determination of the stress-energy tensor. In this paper we determine this tensor by starting with a noncommutative-geometry background and assuming that the static and spherically symmetric spacetime admits conformal motions. This had been established in a previous collaboration with Rahaman et al. using a slightly different approach. Accordingly, the main purpose of this paper is to show that the wormhole obtained can be made stable to linearized radial perturbations.

gr-qc↗
arXiv2016

Gravitational lensing of wormholes in the galactic halo region

A recent study by Rahaman et al. has shown that the galactic halo possesses the necessary properties for supporting traversable wormholes, based on two observational results, the density profile due to Navarro et al. and the observed flat rotation curves of galaxies. Using a method for calculating the deflection angle pioneered by V. Bozza, it is shown that the deflection angle diverges at the throat of the wormhole. The resulting photon sphere has a radius of 0.40 ly. Given the dark-matter background, detection may be possible from past data using ordinary light.

gr-qc↗
arXiv2016

On the stability of thin-shell wormholes

A thin-shell wormhole is theoretically constructible by surgically grafting together two Schwarzschild spacetimes using the so-called cut-and-paste technique. By describing such a wormhole as the limiting case of a spherical shell, it is shown that the structure must be unstable to linearized radial perturbations. Some earlier studies by the author et al. have shown, however, that under certain conditions, thin-shell wormholes can be stable.

gr-qc↗
arXiv2015

Wormholes admitting conformal Killing vectors and supported by generalized Chaplygin gas

When Morris and Thorne first proposed that traversable wormholes may be actual physical objects, they concentrated on the geometry by specifying the shape and redshift functions. This mathematical approach necessarily raises questins regarding the determination of the required stress-energy tensor. This paper discusses a natural way to obtain a complete wormhole solution by assuming that the wormhole (1) is supported by generalized Chaplygin gas and (2) admits conformal Killing vectors.

gr-qc↗
arXiv2014

Revisiting galactic rotation curves given a noncommutative-geometry background

It was shown earlier by Rahaman et al. that a noncommutative-geometry background can account for galactic rotation curves without the need for dark matter. The smearing effect that characterizes noncommutative geometry is described by means of a Gaussian distribution intended to replace the Dirac delta function. The purpose of this paper is two-fold: (1) to account for the galactic rotation curves in a more transparent and intuitively more appealing way by replacing the Gaussian function by the simpler Lorentzian distribution proposed by Nozari and Mehdipour and (2) to show that the smearing effect is both a necessary and sufficient condition for meeting the stability criterion.

gr-qc↗
arXiv2014

Some examples of Hayward wormholes

The first part of this paper discusses a model for the theoretical construction of a simple traversable wormhole with zero density that depends on a preexisting black hole. By assuming the interconvertibilty of black holes and wormholes proposed by S.A. Hayward, it is shown that a toy model suggested by the first model may yield several possible transitions from the preexisting black hole to a wormhole. A final topic is the conversion to a wormhole by assuming a specific model for the exotic matter.

gr-qc↗
arXiv2014

Wormholes supported by a combination of normal and quintessential matter in Einstein and Einstein-Maxwell gravity

It is shown in the first part of this paper that a combined model comprising ordinary and quintessential matter can support a traversable wormhole in Einstein-Maxwell gravity. Since the solution allows zero tidal forces, the wormhole is suitable for a humanoid traveler. The second part of the paper shows that the electric field can be eliminated (Einstein gravity), but only by tolerating enormous tidal forces. Such a wormhole would still be capable of transmitting signals.

gr-qc↗
arXiv2013

Macroscopic wormholes in noncommutative geometry

The purpose of this paper is to show that wormholes in noncommutative geometry can be macroscopic, based in part on an earlier study. The necessary violation of the weak energy condition is attributable to the noncommutative-geometry background rather than to the use of "exotic matter." The zero tidal forces make the wormhole suitable for humanoid travelers. Also discussed is the stability to linearized radial perturbations.

gr-qc↗
arXiv2013

Theoretical construction of stable traversable wormholes

It is shown in this paper that it is possible, at least in principle, to construct a traversable wormhole that is stable to linearized radial perturbations by specifying relatively simple conditions on the shape and redshift functions.

gr-qc↗
arXiv2012

Galactic rotation curves inspired by a noncommutative-geometry background

This paper discusses the observed at rotation curves of galaxies in the context of noncommutative geometry. The energy density of such a geometry is diffused throughout a region due to the uncertainty encoded in the coordinate commutator. This intrinsic property appears to be sufficient for producing stable circular orbits, as well as attractive gravity, without the need for dark matter.

gr-qc↗
arXiv2012

On the stability of thin-shell wormholes in noncommutative geometry

This paper reexamines a special class of thin-shell wormholes that are unstable in general relativity in the framework of noncommutative geometry. It is shown that as a consequence of the intrinsic uncertainty these wormholes are stable to small linearized radial perturbations. Several different spacetimes are considered.

hep-th↗
arXiv2012

On a time-dependent extra spatial dimension

In the usual brane-world scenario matter fields are confined to the four-dimensional spacetime, called a 3-brane, embedded in a higher-dimensional space, usually referred to as the bulk spacetime. In this paper we assume that the 3-brane is a de Sitter space; there is only one extra spatial dimension, assumed to be time dependent. By using the form of the brane-world energy-momentum tensor suggested by Shiromizu et al. in the five-dimensional Einstein equations, it is proposed that the cosmological expansion of the 3-brane may provide a possible explanation for the collapse of the extra dimension, as well as for the energy stored in the resulting curled-up dimension. More precisely, whenever the bulk cosmological constant Λis negative, the extra spatial dimension rapidly shrinks during the inflation of the brane. When Λis positive, on the other hand, the extra spatial dimension either completely follows the cosmological expansion of the brane or completely ignores it, thereby shrinking relative to the expanding space. This behavior resembles the all-or-nothing behavior of ordinary systems in an expanding universe, as recently demonstrated by R.H. Price.

gr-qc↗
arXiv2011

An unexpected topological censor

Morris-Thorne wormholes with a cosmological constant Λhave been studied extensively, even allowing Λto be replaced by a space variable scalar. These wormholes cannot exist, however, if Λis both space and time dependent. Such a Λwill therefore act as a topological censor. While not likely to have a bearing on the present, possible cosmological consequences of inflation cannot be discounted.

gr-qc↗