arXiv subjects

M. Halilsoy

Publications and source records attributed to M. Halilsoy.

At least 73 records · Page 4Linked to original sources

arXiv2014

Fading Hawking Radiation

In this study, we explore a particular type Hawking radiation which ends with zero temperature and entropy. The appropriate black holes for this purpose are the linear dilaton black holes. In addition to the black hole choice, a recent formalism in which the Parikh-Wilczek's tunneling formalism amalgamated with quantum corrections to all orders in \hbar is considered. The adjustment of the coefficients of the quantum corrections plays a crucial role on this particular Hawking radiation. The obtained tunneling rate indicates that the radiation is not pure thermal anymore, and hence correlations of outgoing quanta are capable of carrying away information encoded within them. Finally, we show in detail that when the linear dilaton black hole completely evaporates through such a particular radiation, entropy of the radiation becomes identical with the entropy of the black hole, which corresponds to "no information loss".

gr-qc↗

arXiv2014

Quantum probes of timelike naked singularities in the weak field regime of $f(R)$ global monopole spacetime

The formation of a naked singularity in $f(R)$ global monopole spacetime is considered in view of quantum mechanics. Quantum test fields obeying the Klein$-$Gordon, Dirac and Maxwell equations are used to probe the classical timelike naked singularity developed at $r=0$. We prove that the spatial derivative operator of the fields fails to be essentially self-adjoint. As a result, the classical timelike naked singularity formed in $f(R)$ global monopole spacetime remains quantum mechanically singular when it is probed with quantum fields having different spin structures. Pitelli and Letelier (Phys. Rev. D 80, 104035, 2009) had shown that for quantum scalar ($spin$ $0$% ) probes the general relativistic global monopole singularity remains intact. For specific modes electromagnetic ($spin$ $1$) and Dirac field ($% spin$ $1/2$) probes, however, we show that the global monopole spacetime behaves quantum mechanically regular. The admissibility of this singularity is also incorporated within the Gubser's singularity conjecture.

hep-th↗

arXiv2013

Rindler Modified Schwarzschild Geodesics

The mysterious attractive constant radial force acted in the past on Pioneer spacecrafts - the so-called Pioneer anomaly - is considered within the context of Rindler acceleration. As an idea this is tempting since it is reminiscent of the cosmological constant. Fortunately the anomalous force acts radially toward the sun so that it differs from the mission of a cosmological constant. Without resorting to the physical source responsible for such a term we investigate the modified Schwarzschild geodesics. The Rindler acceleration naturally affects all massive / massless particle orbits. Stable orbits may turn unstable and vice versa with a finely-tuned acceleration parameter. The overall role of the extra term, given its attractive feature is to provide confinement in the radial geodesics.

gr-qc↗

arXiv2013

A new Einstein-nonlinear electrodynamics solution in 2+1-dimensions

We introduce a class of solutions in $2+1-$dimensional Einstein-Power-Maxwell theory for circularly symmetric electric field. The electromagnetic field is considered with an angular component given by $% F_{μν}=E_{0}δ_{μ}^{t}δ_{ν}^{θ}$ for $E_{0}=$ constant. First, we show that the metric for zero cosmological constant and the Power-Maxwell Lagrangian of the form of $\sqrt{\left\vert F_{μν}F^{μν}\right\vert }$, coincides with the solution given in $2+1-$% dimensional gravity coupled with a massless, self interacting real scalar field. With the same Lagrangian and a non-zero cosmological constant we obtain a non-asymptotically flat wormhole solution in $2+1-$dimensions. The confining motions of massive charged and chargeless particles are investigated too. Secondly, another interesting solution is given for zero cosmological constant together with conformal invariant condition. The formation of timelike naked singularity for this particular case is investigated within the framework of the quantum mechanics. Quantum fields obeying the Klein-Gordon and Dirac equations are used to probe the singularity and test the quantum mechanical status of the singularity.

gr-qc↗

arXiv2013

A scan of f(R) models admitting Rindler type acceleration

As a manifestation of large distance effect Grumiller modified Schwarzschild metric with an extraneous term reminiscent of Rindler acceleration. Such a term has the potential to explain the observed flat rotation curves in general relativity. The same idea has been extended herein to the larger arena of $f\left( R\right) $ theory. With particular emphasis on weak energy conditions (WECs) for a fluid we present various classes of $f\left( R\right) $ theories admitting a Rindler-type acceleration in the metric.

gr-qc↗

arXiv2013

Stable thin-shell wormholes with a Chaplygin gas in Einstein-Maxwell-Gauss-Bonnet gravity

We study the stability of thin-shell wormholes in Einstein-Maxwell-Gauss-Bonnet gravity. The equation of state of the thin shell wormhole is considered first to obey a generalized Chaplygin gas and then we generalize it to an arbitrary state function which covers all known cases studied so far. In particular we study the modified Chaplygin gas and give an assessment for a general parotropic fluid. Our study is in d-dimensions and with numerical analysis in d=5 we show the effect of the GB parameter in the stability of thin-shell wormholes against the radial perturbations.

gr-qc↗

arXiv2013

Unified Bertotti-Robinson and Melvin Spacetimes

We present a solution for the Einstein-Maxwell (EM) equations which unifies both the magnetic Bertotti-Robinson (BR) and Melvin (ML) solutions as a single metric in the axially symmetric coordinates ${t,ρ,z,φ} $. Depending on the strength of magnetic field the spacetime manifold, unlike the cases of separate BR and ML spacetime, develops singularity on the symmetry axis ($ρ=0$). Our analysis shows, beside other things that there are regions inaccessible to all null geodesics.

gr-qc↗

arXiv2013

Electromagnetic wave propagation through inhomogeneous material layers

We use Maxwell's equations in a sourceless, inhomogeneous medium with continuous permeability $μ(\mathbf{r}) $ and permittivity $% ε(\mathbf{r}) $ to study the wave propagation. The general form of the wave equation is derived and by virtue of some physical assumptions, including $μ$ and $ε$ as functions of $z,$ the equation has been simplified. Finally by introducing a smooth step dielectric variable we solve the wave equation in the corresponding medium which is in conform with the well known results. Exact double-layer solution in analytic form has been given in terms of the Heun functions.

physics.gen-ph↗

arXiv2013

Charge screening by thin-shells in a 2+1-dimensional regular black hole

We consider a particular Bardeen black hole in 2+1-dimensions. The black hole is sourced by a radial electric field in non-linear electrodynamics (NED). The solution is obtained anew by the alternative Hamiltonian formalism. For $r\rightarrow \infty $ it asymptotes to the charged BTZ black hole. It is shown that by inserting a charged, thin-shell (or ring) the charge of the regular black hole can be screened from the external world.

gr-qc↗

arXiv2013

One dimensional Newton's equation with variable mass

We revisit Newton's equation of motion in one dimension when the moving particle has a variable mass m(x,t) depending both on position (x) and time (t). Geometrically the mass function is identified with one of the metric function in a 1+1-dimensional spacetime. As a reflection of the equivalence principle geodesics equation gives the Newton's law of motion leaving the right hand side to be supplemented by the external forces. The resulting equation involves the speed of light so that our equation of motion addresses a wider scope than the customary classical mechanics. In the limit of infinite light speed which amounts to instantaneous interaction we recover the classical results.

gr-qc↗

arXiv2013

Rindler type acceleration in f(R) gravity

By choosing a fluid source in $f(R)$ gravity, defined by $f\left(R\right) =R-12aξ\ln \left\ | R\right\ | $, where $a$ (=Rindler acceleration) and $ξ$ are both constants, the field equations correctly yield the Rindler acceleration term in the metric. We identify domains in which the weak energy conditions (WEC) and the strong energy conditions (SEC) are satisfied.

physics.gen-ph↗

arXiv2013

Existence of Reissner-Nordstrom type black holes in f(R) gravity

We investigate the existence of Reissner-Nordström (RN) type black holes in f(R) gravity. Our emphasis is to derive, in the presence of electrostatic source, the necessary conditions which provide such static, spherically symmetric (SSS) black holes available in f(R) gravity. We also study the thermodynamics of the black hole solution.

gr-qc↗

arXiv2013

Double-bounce domain-wall in Einstein-Yang-Mills-Scalar black holes

We find Einstein-Yang-Mills (EYM) black hole solutions endowed with massless scalar hair in the presence of a potential $V\left(ϕ\right) $ as function of the scalar field $ϕ$. Choosing $V\left(ϕ\right) =$constant (or zero) sets the scalar field to vanish leaving us with the EYM black holes. Our class of black hole solutions is new so that they do not asymptote in general to any known limits. Particular case is given, however, which admits an asymptotically anti de Sitter limit in $6-$dimensional spacetime. The role of the potential $V\left(ϕ\right) $ in making double bounces (i.e. both a minimum and maximum radii) on a Domain Wall (DW) universe is highlighted.

gr-qc↗

arXiv2012

Comment on "Static and spherically symmetric black holes in f(R) theories"

We consider the interesting "near-horizon test" reported in (PRD84, 084006(2011), arXiv:1107.5727) for any static, spherically symmetric (SSS) black hole solution admitted in f(R) gravity. Before adopting the necessary conditions for the test, however, revisions are needed as we point out in this Comment.

gr-qc↗

arXiv2012

Necessary conditions for having wormholes in f(R) gravity

For a generic $f(R)$ which admits a polynomial expansion of at least third order (i.e. $\frac{d^{3}f}{dR^{3}}\neq 0$) we find the near-throat wormhole solution. Necessary conditions for the existence of wormholes in such $f(R)$ theories are derived for both zero and non-zero matter sources. A particular choice of energy-momentum reveals that the wormhole geometry satisfies the weak energy condition (WEC). For a range of parameters even the strong energy condition (SEC) is shown to be satisfied.

gr-qc↗

arXiv2012

Black hole and thin-shell wormhole solutions in Einstein-Hoffman-Born-Infeld theory

We employ an old field theory model, formulated and discussed by Born, Infeld, Hoffman and Rosen during 1930s. Our method of cutting-gluing of spacetimes resolves the double-valuedness in the displacement vector D(E), pointed out by these authors. A characteristic feature of their model is to contain a logarithmic term, and by bringing forth such a Lagrangian anew, we aim to attract the interest of field theorists to such a Lagrangian. We adopt the Hoffman-Born-Infeld (HBI) Lagrangian in general relativity to construct black holes and investigate the possibility of viable thin-shell wormholes. In particular, the stability of thin-shell wormholes supported by normal matter in 5-dimensional Einstein-HBI-Gauss-Bonnet gravity is highlighted.

gr-qc↗

arXiv2012

2+1-dimensional electrically charged black holes in Einstein - Power Maxwell Theory

A large family of new black hole solutions in 2+1-dimensional Einstein-Power-Maxwell (EPM) gravity with prescribed physical properties is derived. We show with particular examples that according to the power parameter k of the Maxwell field, the obtained solutions may be asymptotically flat for 1/2 1 in the vanishing cosmological constant limit. We study the thermodynamic properties of the solution with two different models and it is shown that thermodynamic quantities satisfy the first law. The behaviour of the heat capacity indicates that by employing the 1+1-dimensional dilaton analogy the local thermodynamic stability is satisfied.

gr-qc↗

arXiv2012

'Square Root' of the Maxwell Lagrangian versus confinement in general relativity

We employ the 'square root' of the Maxwell Lagrangian (i.e. \surd(F_{μν}F^{μν})), coupled with gravity to search for the possible linear potentials which are believed to play role in confinement. It is found that in the presence of magnetic charge no confining potential exists in such a model. Confining field solutions are found for radial geodesics in pure electrically charged Nariai- Bertotti-Robinson (NBR)-type spacetime with constant scalar curvature. Recently, Guendelman, Kaganovich, Nissimov and Pacheva, [Phys.Lett.B704(2011)230] have shown that superposed square root with standard Maxwell Lagrangians yields confining potentials in spherically symmetric spacetimes with new generalized Reissner-Nordström-de Sitter / -anti-de Sitter black hole solutions. In NBR spacetimes we show that confining potentials exist even when the standard Maxwell Lagrangian is relaxed.

gr-qc↗