WORMHOLES OF K-ESSENCE IN ARBITRARY SPACE–TIME DIMENSIONS

2008 ◽  
Vol 23 (20) ◽  
pp. 3165-3175 ◽  
Author(s):  
J. ESTEVEZ-DELGADO ◽  
T. ZANNIAS
Keyword(s):  
Energy Momentum Tensor ◽  
Opposite Sign ◽  
Momentum Tensor ◽  
Space Time ◽  
Parameter Family ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Asymptotically Flat ◽  
Arbitrary Space ◽  
Two Parameter

We consider a K-essence involving a massless scalar field Φ minimally coupled to Einstein gravity in D ≥ 4 space–time dimensions. This theory admits a two-parameter family of spherical wormholes representing two asymptotically-flat universes connected via a (D-2)-dimensional spherical throat. The ADM masses of the two ends are unequal and of opposite sign except for a one-parameter family where both ends possess vanishing ADM masses. By cut and paste techniques, we construct a two-parameter family of wormholes where the ends possess equal and positive ADM masses but the throat is a (D-1)-dimensional thin-shell. The structure of the surface energy–momentum tensor is also analyzed.

On the origin of black hole evaporation radiation

1976 ◽  
Vol 351 (1664) ◽  
pp. 129-139 ◽  
Keyword(s):  
Black Hole ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Static Vacuum ◽  
Black Hole Evaporation ◽  
A Value ◽  
Special Case ◽  
Collapse Process

The physical basis underlying the black hole evaporation process is clarified by a calculation of the expectation value of the energy-momentum tensor for a massless scalar field in a completely general two dimensional collapse scenario. It is found that radiation is produced inside the collapsing matter which propagates both inwards and outwards. The ingoing com­ponent eventually emerges from the star after travelling through the centre. The outgoing energy flux appears at infinity as the evaporation radiation discovered by Hawking. At late times, outside the star, the former component fades out exponentially, and the latter component approaches a value which is independent of the details of the collapse process. In the special case of a collapsing hollow, thin shell of matter, all the radiation is produced at the shell. These results are independent of regularization ambiguities, which enter only the static vacuum polariza­tion terms in the energy-momentum tensor. The significance of an earlier remark about black hole explosions is discussed in the light of these results.

Vacuum polarization in the background of conical singularity

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040030
Author(s):  
Yuri V. Grats ◽  
Pavel Spirin
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Energy Momentum Tensor ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Momentum Tensor ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Dimensional Spacetime ◽  
Higher Dimensional

We consider the gravity-induced effects associated with a massless scalar field living in a higher-dimensional spacetime being the tensor product of Minkowski space and spherically-symmetric space with angle deficit. These spacetimes are considered as simple models for a multidimensional global monopole or cosmic string with flat extra dimensions, where the deficit of solid angle is proportional to Newton constant and tension. Thus, we refer to them as conical backgrounds. In terms of the angular deficit value, we derive the perturbative expression for the scalar Green’s function and compute it to the leading order. With the use of this Green’s function we compute the renormalized vacuum expectation value of the scalar-field’s energy-momentum tensor. We make some general note on the linear-on-curvature part of the trace of even coefficients of Schwinger-deWitt expansion.

scholarly journals Examining a covariant and renormalizable quantum field theory in de Sitter space by studying “black hole radiation”

2016 ◽  
Vol 31 (11) ◽  
pp. 1650052 ◽  
Author(s):  
Hamed Pejhan ◽  
Surena Rahbardehghan
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Black Hole ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Quantum Field ◽  
De Sitter ◽  
Black Hole Radiation

Respecting that any consistent quantum field theory in curved space–time must include black hole radiation, in this paper, we examine the Krein–Gupta–Bleuler (KGB) formalism as an inevitable quantization scheme in order to follow the guideline of the covariance of minimally coupled massless scalar field and linear gravity on de Sitter (dS) background in the sense of Wightman–Gärding approach, by investigating thermodynamical aspects of black holes. The formalism is interestingly free of pathological large distance behavior. In this construction, also, no infinite term appears in the calculation of expectation values of the energy–momentum tensor (we have an automatic and covariant renormalization) which results in the vacuum energy of the free field to vanish. However, the existence of an effective potential barrier, intrinsically created by black holes gravitational field, gives a Casimir-type contribution to the vacuum expectation value of the energy–momentum tensor. On this basis, by evaluating the Casimir energy–momentum tensor for a conformally coupled massless scalar field in the vicinity of a nonrotating black hole event horizon through the KGB quantization, in this work, we explicitly prove that the hole produces black-body radiation which its temperature exactly coincides with the result obtained by Hawking for black hole radiation.

scholarly journals Cosmological reconstruction of f(T, 𝒯) gravity

2014 ◽  
Vol 11 (08) ◽  
pp. 1450077 ◽  
Author(s):  
Davood Momeni ◽  
Ratbay Myrzakulov
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Chaplygin Gas ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Two Fluids ◽  
Consistent Model ◽  
The Universe

Motivated by the newly proposal for gravity as the effect of the torsion scalar T and trace of the energy momentum tensor 𝒯, we investigate the cosmological reconstruction of different models of the Universe. Our aim here is to show that how this modified gravity model, f(T, 𝒯) is able to reproduce different epochs of the cosmological history. We explicitly show that f(T, 𝒯) can be reconstructed for ΛCDM as the most popular and consistent model. Also we study the mathematical reconstruction of f(T, 𝒯) for a flat cosmological background filled by two fluids mixture. Such model describes phantom–non-phantom era as well as the purely phantom cosmology. We extend our investigation to more cosmological models like perfect fluid, Chaplygin gas and massless scalar field. In each case we obtain some specific forms of f(T, 𝒯). These families of f(T, 𝒯) contain arbitrary function of torsion and trace of the energy momentum.

scholarly journals Scalar Casimir effect in a high-dimensional cosmic dispiration spacetime

2018 ◽  
Vol 27 (12) ◽  
pp. 1850107 ◽  
Author(s):  
H. F. Mota ◽  
E. R. Bezerra de Mello ◽  
K. Bakke
Keyword(s):  
Cosmic String ◽  
Energy Momentum Tensor ◽  
Casimir Effect ◽  
Topological Defects ◽  
Vacuum Expectation ◽  
Scalar Fields ◽  
Momentum Tensor ◽  
High Dimensional ◽  
Massless Scalar ◽  
Massless Scalar Field

In this paper we present a complete and detailed analysis of the calculation of both the Wightman function and the vacuum expectation value of the energy–momentum tensor that arise from quantum vacuum fluctuations of massive and massless scalar fields in the cosmic dispiration spacetime, which is formed by the combination of two topological defects: a cosmic string and a screw dislocation. This spacetime is obtained in the framework of the Einstein–Cartan theory of gravity and is considered to be a chiral spacelike cosmic string. For completeness we perform the calculation in a high-dimensional spacetime, with flat extra dimensions. We found closed expressions for the energy–momentum tensor and, in particular, in [Formula: see text]-dimensions, we compare our results with previous existing ones in the literature for the massless scalar field case.

scholarly journals Limits on the Validity of the Semiclassical Theory — A Minisuperspace Example

1997 ◽  
Vol 06 (03) ◽  
pp. 363-375
Author(s):  
L. Sriramkumar
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Matter Field ◽  
Massless Scalar ◽  
Back Reaction ◽  
Massless Scalar Field ◽  
Semiclassical Theory ◽  
Dimensionless Quantity ◽  
Complete Field

For want of a more natural proposal, it is generally assumed that the back-reaction of a quantized matter field on a classical metric is given by the expectation value of its energy–momentum tensor, evaluated in a specified state. This semiclassical theory can be reliable only when the fluctuations in the energy–momentum densities of the quantum field are negligible. Based on this condition, Kuo and Ford have constructed a dimensionless quantity, whose magnitude reflects the amount of fluctuation in the back-reaction term and hence on the validity of the semiclassical theory. In this paper, we evaluate this quantity for the minisuperspace model of a quantized massless scalar field in a Friedmann universe. We conclude that the semiclassical theory for the model we consider here can be relied upon only if the scalar field is in states like coherent states. The implications of our investigation on the complete field theory are also discussed.

CASIMIR EFFECT FOR THE ROBIN SURFACES IN STATIC ROBERTSON–WALKER SPACE–TIME

2011 ◽  
Vol 20 (02) ◽  
pp. 161-168 ◽  
Author(s):  
MOHAMMAD R. SETARE ◽  
M. DEHGHANI
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Casimir Effect ◽  
Vacuum Expectation ◽  
Robin Boundary Condition ◽  
Momentum Tensor ◽  
Space Time ◽  
Conformally Invariant ◽  
Time Space ◽  
Robin Boundary

We investigate the energy–momentum tensor for a massless conformally coupled scalar field in the region between two curved surfaces in k = -1 static Robertson–Walker space–time. We assume that the scalar field satisfies the Robin boundary condition on the surfaces. Robertson–Walker space–time space is conformally related to Rindler space; as a result we can obtain vacuum expectation values of the energy–momentum tensor for a conformally invariant field in Robertson–Walker space–time space from the corresponding Rindler counterpart by the conformal transformation.

scholarly journals Positive Energy Driven CTCs In ADM 3+1 Space – Time of Unprotected Chronology

2021 ◽  
Author(s):  
Deep Bhattacharjee
Keyword(s):  
Energy Density ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Space Time ◽  
Exotic Matter ◽  
Positive Energy ◽  
Spacelike Hypersurfaces ◽  
Stress Energy ◽  
Maxwell Fields ◽  
Stress Energy Momentum Tensor

Chronology unprotected mechanisms are considered with a very low gravitational polarization to make the wormhole traversal with positive energy density everywhere. No need of exotic matter has been considered with the assumption of the Einstein-Dirac-Maxwell Fields, encountering above the non-zero stress-energy-momentum tensor through spacelike hypersurfaces by a hyperbolic coordinate shift.

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