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Kimet Jusufi

Publications and source records attributed to Kimet Jusufi.

At least 127 records · Page 7Linked to original sources
arXiv2018

Gravitational Lensing by Rotating Wormholes

In this paper the deflection angle of light by a rotating Teo wormhole spacetime is calculated in the weak limit approximation. We mainly focus on the weak deflection angle by revealing the gravitational lensing as a partially global topological effect. We apply the Gauss-Bonnet theorem (GBT) to the optical geometry osculating the Teo-Randers wormhole optical geometry to calculate the deflection angle. Furthermore we find the same result using the standard geodesic method. We have found that the deflection angle can be written as a sum of two terms, namely the first term is proportional to the throat of the wormhole and depends entirely on the geometry, while the second term is proportional to the spin angular momentum parameter of the wormhole. A direct observation using lensing can shed light and potentially test the nature of rotating wormholes by comparing with the black holes systems.

gr-qc↗
arXiv2017

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 [Class. Quant. Grav. 25, 235009 (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.

gr-qc↗
arXiv2017

Stability of Effective Thin-shell Wormholes Under Lorentz Symmetry Breaking Supported by Dark Matter and Dark Energy

In this paper, we construct generic, spherically symmetric thin-shell wormholes and check their stabilities using the unified dark sector, including dark energy and dark matter. We give a master equation, from which one can recover, as a special case, other stability solutions for generic spherically symmetric thin-shell wormholes. In this context, we consider a particular solution; namely we construct an effective thin-shell wormhole under Lorentz symmetry breaking. We explore stability analyses using different models of the modified Chaplygin gas with constraints from cosmological observations such as seventh-year full Wilkinson microwave anisotropy probe data points, type Ia supernovae, and baryon acoustic oscillation. In all these models we find stable solutions by choosing suitable values for the parameters of the Lorentz symmetry breaking effect.

gr-qc↗
arXiv2017

Quantum Tunneling and Quasinormal Modes in the Spacetime of Alcubierre Warp Drive

In a seminal paper, Alcubierre showed that Einstein's theory of general relativity appears to allow a super-luminal motion. In the present study, we use a recent eternal-warp-drive solution found by Alcubierre to study the effect of Hawking radiation upon an observer located within the warp drive in the framework of the quantum tunneling method. We find the same expression for the Hawking temperatures associated with the tunneling of both massive vector and scalar particles, and show this expression to be proportional to the velocity of the warp drive. On the other hand, since the discovery of gravitational waves, the quasinormal modes (QNMs) of black holes have also been extensively studied. With this puprpose in mind, we perform a QNM analysis of massive scalar field perturbations in the background of the eternal-Alcubierre-warp-drive (EAWD) spacetime. Our analytical analysis shows that massive scalar perturbations lead to stable QNMs.

gr-qc↗
arXiv2017

Stability of a $d$-dimensional thin-shell wormhole surrounded by quintessence

We study the stability of different higher dimensional thin--shell wormholes (HDTSW) in general relativity with a cosmological constant. We show that a $d$--dimensional thin--shell wormhole surrounded by quintessence can have three different throat geometries: spherical, planar and hyperbolic. Unlike the spherical geometry, the planar and hyperbolic geometries allow different topologies that can be interpreted as higher-dimensional domain walls or branes connecting two universes. To construct these geometries, we use the cut-and-paste procedure by joining two identical vacuum spacetime solutions. Properties such as the null energy condition and geodesics are also studied. A linear stability analysis around the static solutions is carried out. Our stability analysis takes into account a more general HDTSW geometry than previous works so it is possible to recover other well-known stability HDTSW conditions.

gr-qc↗
arXiv2017

Light deflection by charged wormholes in Einstein-Maxwell-dilaton theory

In this paper, we study the deflection of light by a class of charged wormholes within the context of the Einstein-Maxwell-dilaton theory. The primordial wormholes are predicted to exist in the early universe, where inflation driven by the dilaton field. We perform our analysis through optical geometry using the Gibbons-Werner method (GW), by adopting the Gauss-Bonnet theorem and the standard geodesics approach. We report an interesting result for the deflection angle in leading-order terms--namely, the deflection angle increases due to the electric charge $Q$ and the magnetic charge $P$, whereas it decreases due to the dilaton charge $Σ$. Finally, we confirm our findings by means of geodesics equations. Our computations show that the GW method gives an exact result in leading order terms.

gr-qc↗
arXiv2017

Stable Dyonic Thin-Shell Wormholes in Low-Energy String Theory

Considerable attention has been devoted to the wormhole physics in the past 30 years by exploring the possibilities of finding traversable wormholes without the need of exotic matter. In particular the thin-shell wormhole formalism has been widely investigated by exploiting the cut-and-paste technique to merge two space-time regions and, to research the stability of these wormholes developed by Visser. This method helps us to minimize the amount of the exotic matter. In this paper we construct a four dimensional, spherically symmetric, dyonic thin-shell wormhole with electric charge $Q$, magnetic charge $P$, and dilaton charge $Σ$, in the context of Einstein-Maxwell-dilaton theory. We have applied Darmois-Israel formalism and the cut-and-paste method by joining together two identical spacetime solutions. We carry out the dyonic thin-shell wormhole stability analyses by using a linear barotropic gas, Chaplygin gas, and logarithmic gas for the exotic matter. It is shown that by choosing suitable parameter values as well as equation of state parameter, under specific conditions we obtain a stable dyonic thin-shell wormhole solution. Finally we argue that, the stability domain of the dyonic thin-shell wormhole can be increased in terms of electric charge, magnetic charge, and dilaton charge.

gr-qc↗
arXiv2017

Charged Thin-shell Gravastars in Noncommutative Geometry

In this paper we construct a charged thin-shell gravastar model within the context of noncommutative geometry. To do so, we choose the interior of the nonsingular de Sitter spacetime with an exterior charged noncommutative solution by cut-and-paste technique and apply the generalized junction conditions. We then investigate the stability of a charged thin-shell gravastar under linear perturbations around the static equilibrium solutions as well as the thermodynamical stability of the charged gravastar. We find the stability regions by choosing appropriate parameter values which is located sufficiently close to the event horizon.

gr-qc↗
arXiv2017

Deflection Angle of Light by Wormholes using the Gauss-Bonnet Theorem

In this letter, we have investigated the deflection angle of light by wormholes using a new geometrical method known as Gibbons-Werner method (GW). In particular we have calculated the deflection angle of light in the weak limit approximation in two wormhole spacetime geometries: Ellis wormhole and Janis-Newman-Winnicour (JNW) wormhole. We have employed the famous Gauss-Bonnet theorem (GBT) to the Ellis wormhole optical geometry and JNW wormhole optical geometry, respectively. By using GBT, we computed the deflection angles in leading orders by these wormholes and our results were compared with the ones in the literature.

gr-qc↗
arXiv2017

Effect of Lorentz Symmetry Breaking on the Deflection of Light in a Cosmic String Spacetime

We investigate the Lorentz symmetry breaking effects (LSBE) on the deflection of light by a rotating cosmic string spacetime in the weak limit approximation. We first calculate the deflection angle by a static cosmic string for a fixed spacelike 4-vector case (FSL) with the corresponding effective-string optical metric using the Gauss-Bonnet theorem (GBT). Then, we focus on a more general scenario, namely we calculate the deflection angle by a rotating cosmic string applying the GBT to Randers effective-string metric. We obtain a significant modification in the deflection angle because of the LSBE parameter. We find a first and second order correction terms due to the global effective topology which are proportional to the cosmic string and LSBE parameter, respectively. Finally, for a fixed time-like 4-vector (FTL) case, we show that the deflection angle is not affetced by LSBE parameter.

gr-qc↗
arXiv2017

The Effect of GUP to Massive Vector and Scalar Particles Tunneling From a Warped DGP Gravity Black Hole

This paper discusses the effects of the mass and the angular momentum of massive vector and scalar particles on the Hawking temperature manifested under the effects of the generalized uncertainty principle (GUP). In particular, we calculate the Hawking temperature of a black hole in a warped DGP gravity model in the framework of the quantum tunneling method. We use the modified Proca and Klein-Gordon equations previously determined from the GUP Lagrangian in the spacetime background of a warped Dvali-Gabadadze-Porrati (DGP) metric, with the help of Hamilton-Jacobi (HJ) and semiclassical (WKB) approximation methods. We find that as a special case of a warped DGP black hole solution, the Hawking temperature of a Schwarzschild-de Sitter (SdS) black hole can be determined. Furthermore, the Hawking temperature is influenced by the mass and the angular momentum of vector and scalar particles and depends on which of those types of particles is being emitted by the black hole. We conclude that the nonthermal nature of the Hawking spectrum leads to Planck-scale nonthermal correlations, shedding light on the information paradox in black hole evaporation.

physics.gen-ph↗
arXiv2017

Tunneling of Massive/Massless Bosons From the Apparent Horizon of FRW Universe

In this article we investigate the Hawking radiation of vector particles from the apparent horizon of a Friedmann-Robertson-Walker (FRW) universe in the framework of quantum tunneling method. Furthermore we use Proca equation, a relativistic wave equation for a massive/massless spin-1 particle (massless $γ$ photons, weak massive $W^{\pm}$ and $Z^{0}$ bosons, strong massless gluons and $ρ$ and $ω$ mesons) together with a Painlevé spacetime metric for the FRW universe. We solve the Proca equation via Hamilton-Jacobi (HJ) equation and the WKB approximation method. We recover the same result for the Hawking temperature associated with vector particles as in the case of scalar and Dirac particles tunnelled from outside to the inside of the apparent horizon in a FRW universe.

gr-qc↗
arXiv2017

Quantum Effects on the Deflection of Light and the Gauss-Bonnet Theorem

In this letter we apply the Gauss--Bonnet theorem (GB) to calculate the deflection angle by a quantum corrected Schwarzschild black hole in the weak limit approximation. In particular we calculate the light deflection by two types of quantum corrected black holes: the renormalization group improved Schwarzschild solution and the quantum corrected Schwarzschild solution in Bohmian quantum mechanics. We start from the corresponding optical metrics to use then the GB theorem and calculate the Gaussian curvature in both cases. We calculate the leading terms of the deflection angle and show that quantum corrections modifies the deflection angle in both solutions. Finally by performing geodesics calculations we show that GB method gives exact results in leading order terms.

gr-qc↗
arXiv2017

Light Deflection by a Rotating Global Monopole Spacetime

We investigate the deflection of light by a rotating global monopole spacetime and a rotating Letelier spacetime in the weak deflection approximation. To this end, we apply the Gauss-Bonnet theorem to the corresponding osculating optical geometries and show that the deflection of light increases due to the presence of the global monopole parameter and the string cloud parameter, respectively. The results obtained for the deflection angle in the equatorial plane generalize known results for the corresponding non-rotating global monopole and Letelier spacetimes as well as the Kerr solution.

gr-qc↗
arXiv2017

Hawking radiation of scalar and vector particles from 5D Myers-Perry black holes

In the present paper we explore the Hawking radiation as a quantum tunneling effect from a rotating 5 dimensional Myers-Perry black hole (5D-MPBH) with two independent angular momentum components. First, we investigate the Hawking temperature by considering the tunneling of massive scalar particles and spin-1 vector particles from the 5D-MPBH in the Painlevé coordinates and then in the corotating frames. More specifically, we solve the Klein-Gordon and Proca equations by applying the WKB method and Hamilton-Jacobi equation in both cases. Finally, we recover the Hawking temperature and show that coordinates systems do not affect the Hawking temperature.

gr-qc↗
arXiv2017

Canonical Acoustic Thin-Shell Wormholes

In this paper we model a canonical acoustic thin shell wormhole (CATSW) in the framework of analogue gravity systems. In this model we apply cut and paste technique to join together two spherically symmetric, analogue canonical acoustic solutions, and compute the analogue surface density/surface pressure of the fluid using the Darmois- Israel formalism. We study the stability analyses by using a linear barotropic fluid (LBF), chaplygin fluid (CF), logarithmic fluid (LogF), polytropic fluid (PF), and finally Van der Waals Quintessence (VDWQ). We show that a kind of analog acoustic fluid with negative energy is required at the throat to keep the wormhole stable. It is argued that, CATSW can be a stabile thin-shell wormhole if we choose a suitable parameter values.

physics.gen-ph↗
arXiv2017

Quantum Tunneling of Spin-1 Particles from a 5D Einstein-Yang-Mills-Gauss-Bonnet Black Hole Beyond Semiclassical Approximation

In the present paper we study the Hawking radiation as a quantum tunneling effect of spin-$1$ particles from a five-dimensional, spherically symmetric, Einstein-Yang-Mills-Gauss-Bonnet (5D EYMGB) black hole. We solve the Proca equation (PE) by applying the WKB approximation and separation of variables via Hamilton-Jacobi (HJ) equation which results in a set of five differential equations, and reproduces in this way, the Hawking temperature. In the second part of this paper, we extend our results beyond the semiclassical approximation. In particular, we derive the logarithmic correction to the entropy of the 5D EYMGB black hole and show that the quantum corrected specific heat indicates the possible existence of a remnant.

gr-qc↗