Semiclassical Gravitational Effects Research Articles

Semiclassical gravitational effects on the gravitational lensing in the spacetime of topological defects

The theory of gravitational lensing has revealed many generic and fundamental properties of compact objects like black holes and wormholes. In this article, we utilize a recent formulation to compute the quantum effects on the deflection angle of a light ray, namely, the Gauss–Bonnet theorem (GBT) to explore the semiclassical gravitational effects in the spacetime of a point-like global monopole and a cosmic string. Previously, the Gauss–Bonnet theorem (Gibbons and Werner, 2008) was proposed as an alternative way to compute the deflection angle of light in a static, spherically symmetric and asymptotically flat spacetime. In the present article we have used the celebrated GBT that applied to the optical metric as well as the geodesic method in computing the deflection angle. Interestingly one can observe that we have found an exact result between GBT and the standard approach up to the third-order contributions terms by modifying the domain of integration for cosmic string and global monopole deflection angles. Finally we have considered the time delay in the cosmic string/global monopole spacetime and found that the delay in time is proportional to the linear mass density of the cosmic string and global monopole parameter, respectively.

Analog model for light propagation in semiclassical gravity

We treat a model based upon nonlinear optics for the semiclassical gravitational effects of quantum fields upon light propagation. Our model uses a nonlinear material with a nonzero third order polarizability. Here a probe light pulse satisfies a wave equation containing the expectation value of the squared electric field. This expectation value depends upon the presence of lower frequency quanta, the background field, and modifies the effective index of refraction, and hence the speed of the probe pulse. If the mean squared electric field is positive, then the pulse is slowed, which is analogous to the gravitational effects of ordinary matter. Such matter satisfies the null energy condition and produces gravitational lensing and time delay. If the mean squared field is negative, then the pulse has a higher speed than in the absence of the background field. This is analogous to the gravitational effects of exotic matter, such as stress tensor expectation values with locally negative energy densities, which lead to repulsive gravitational effects, such as defocusing and time advance. We give some estimates of the magnitude of the effects in our model and find that they may be large enough to be observable. We also briefly discuss the possibility that the mean squared electric field could be produced by the Casimir vacuum near a reflecting boundary.

SEMICLASSICAL GRAVITATIONAL EFFECTS AROUND GLOBAL MONOPOLE IN BRANS–DICKE THEORY

Recently, W. A. Hiscock4studied the semi classical gravitational effects around global monopole. He obtained the vacuum expectation value of the stress–energy tensor of an arbitrary collection of conformal mass less free quantum fields (scalar, spinor and vectors) in the spacetime of a global monopole. With this stress–energy tensor, we study the semiclassical gravitational effects of a global monopole in the context of Brans–Dicke theory of gravity.

Semiclassical gravitational effects near a singular magnetic flux

We consider the backreaction of the vacuum polarization effect for a massive charged scalar field in the presence of a singular magnetic massless string on the background metric. Using semiclassical approach, we find the first-order (in ℏ units) metric modifications and the corresponding gravitational potential and deficit angle. It is shown that, in certain region of values of coupling constant and magnetic flux, the gravitational potential and deficit angle can be positive as well as negative over all distances from the string and can even change its sign. Unlike the case of massless scalar field, the gravitational corrections were found to have short-range behavior.

Semi classical gravitational effects around global monopole in Kalb-Ramond background

The problem of semiclassical gravitational effects of globalmonopole in Kalb-Ramond backgroundinvestigated. It is shown that the monopoleexerts repulsive gravitational force on nonrelativistic matter and space around it hasa deficit solid angle.

Semi-classical gravitational effects around global monopoles in Lyra geometry

W.A. Hiscock (1990, Class. Quantum Gravitation 7, L235) obtained the vacuum expectation value of the stress-energy tensor of an arbitrary collection of conformal massless free quantum fields (scalar, spinor and vectors) in the space-time of a static global monopole. With this stress-energy tensor, the semi-classical Einstein equations are solved retaining terms up to first order in ħ in Lyra geometry.

MOTION OF TEST PARTICLES AROUND GAUGE MONOPOLES OR NEAR COSMIC STRINGS CONSIDERING SEMICLASSICAL GRAVITATIONAL EFFECTS

In this paper, we have studied the motion of test particles near cosmic strings as well as around gauge monopoles with semiclassical gravitational effects. In case of cosmic strings, the nature of the trajectory of the test particle has changed due to the semiclassical effects while for gauge monopole the trajectory has no effect due to the semiclassical consideration.

Semiclassical gravitational effects in de Sitter space at finite temperature

In the framework of finite-temperature conformal scalar field theory on de Sitter spacetime the linearized Einstein equations for the renormalized stress tensor are solved exactly. In this theory quantum field fluctuations are concentrated near two spheres of the de Sitter radius, propagating as light wavefronts. The analysis, performed for a flat expanding universe, shows exponential damping of the back-reaction effects far from these spherical objects. The solutions obtained for the semiclassical Einstein equations in a de Sitter background can also be extended straightforwardly to the anti-de-Sitter geometry.

Semiclassical gravitational effects in the spacetime of a rotating cosmic string.

Semiclassical gravitational effects in the spacetime of a rotating cosmic string.

Semiclassical gravitational effects near cosmic strings

The vacuum expectation value of the stress-energy tensor of an arbitrary collection of conformal massless free quantum fields (scalar, spinor, and vector) in the presence of a static, cylindrically symmetric cosmic string is found, up to an undetermined numerical constant. This quantum stress-energy tensor is then used as a source in the linearized semiclassical Einstein equations, which are solved to find the first-order (in Ł) corrections to the exterior metric of a static, cylindrically symmetric cosmic string. The main result is that, at first-order in Ł, the ( r, ø) two-space is no longer a simple flat cone; to this order the ( r, ø) two- space is a (linearized) hyperboloid, which asymptotically approaches the classical conical surface at large values of r. The asymptotic value of the deficit angle of the cone is unchanged, still being precisely 8 πμ.

Gravitation, Phase Transitions, and the Big Bang

Introduced here is a model of the early universe based on the possibility of a first-order phase transition involving gravity, and arrived at by a consideration of instabilities in the semiclassical theory. The evolution of the system is very different from the standard Friedmann-Robertson-Walker big-bang scenario, indicating the potential importance of semiclassical finite-temperature gravitational effects. Baryosynthesis and monopole production in this scenario are also outlined.