Yazar "Halilsoy, Mustafa" seçeneğine göre listele
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Yayın 2+1-dimensional electrically charged black holes in Einstein - Power Maxwell Theory(APS Physics, 2010) Gürtuğ, Özay; Mazharimousavi, S. Habib; Halilsoy, Mustafa; Gürtuğ, ÖzayA large family of new black hole solutions in 2 + 1 -dimensional Einstein-power-Maxwell 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 < k < 1 or nonflat for k > 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 behavior of the heat capacity indicates that by employing the 1 + 1 -dimensional dilaton analogy the local thermodynamic stability is satisfied.Yayın The charged Zipoy–Voorhees metric with astrophysical applications(The European Physical Journal C, 2022) Gürtuğ, Özay; Halilsoy, Mustafa; Mangut, Mert; Gürtuğ, ÖzayStarting from an integral of the interaction region of colliding Einstein–Maxwell waves and by applying a coordinate transformation, we obtain the charged version of the static Zipoy–Voorhees (Z V) metric valid for all values of the distortion parameter ? . In Schwarzschild coordinates, we investigate the effect of the charge in the newly found spacetime, stress the analogy with Reissner–Nordstrom metric and discuss some of its features. It is shown that from the expression of Weyl curvature, directional singularities become manifest. For astrophysical importance, we find lensing of null geodesics from the Gauss–Bonnet theorem in such non-spherically charged objects. To prepare the ground for our null, circular geodesics we consider the angular equation linearized about the symmetry plane ? = ?/2. This, in turn, suggests the distortion parameter (the Z V parameter) must be in the interval 1/2Yayın Colliding wave solutions in a symmetric non-metric theory(Springerlink, 2008) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayA method is given to generate the non-linear interaction (collision) of linearly polarized gravity coupled torsion waves in a non-metric theory. Explicit examples are given in which strong mutual focussing of gravitational waves containing impulsive and shock components coupled with torsion waves does not result in a curvature singularity. However, the collision of purely torsion waves displays a curvature singularity in the region of interaction.Yayın Effect of NUT parameter on the analytic extension of the Cauchy horizon that develop in colliding wave spacetimes(WorldScientific, 2009) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayThe Cauchy horizon forming colliding wave solution due to Chandrasekhar and Xanthopoulos (CX) has been generalized by inclusion of the NUT ( Newman - Unti - Tamburino) parameter. This is done by transforming the part of the inner horizon region of a Kerr-Newman-NUT black hole into the space of colliding waves. By taking appropriate combination of Killing vectors and analytically extending beyond the Cauchy horizon the time-like hyperbolic sigularities are resolved as well. This provides another example of its kind among the type - D metrics with special emphasis on the role of the NUT parameter. Finally, it is shown that horizons of colliding higher dimensional plane waves obtained from the black p-branes undergoes a similar procedure of analytic extension.Yayın The effect of sources on the inner horizon of black holes(APS Physics, 2001) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzaySingle pulse of null dust and colliding null dusts both transform a regular horizon into a space-like singularity in the space of colliding waves. The local isometry between such space-times and black holes extrapolates these results to the realm of black holes. However, inclusion of particular scalar fields instead of null dusts creates null singularities rather than space-like ones on the inner horizons of black holes.Yayın Failure of a stability conjecture in general relativity(Springerlink, 2002) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayBy employing an exact back-reaction geometry, Helliwell-Konkowski stability conjecture is shown to fail. This happens when a test null dust is inserted to the interaction region of cross-polarized Bell-Szekeres spacetime.Yayın Generating static spherically symmetric black-holes in lovelock gravity(WorldScientific, 2009) Mazharimousavi, S. Habib; Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayGeneralization of a known theorem to generate static, spherically symmetric black-hole solutions in higher dimensional Lovelock gravity is presented. Particular limits, such as Gauss-Bonnet (GB) and/or Einstein-Hilbert (EH) in any dimension N yield all the solutions known to date with an energy-momentum. In our generalization, with special emphasis on the third order Lovelock gravity, we have found two different class of solutions characterized by the matter field parameter. Several particular cases are studied and properties related to asymptotic behaviours are discussed. Our general solution which covers topological black holes as well, splits naturally into distinct classes such as Chern-Simon (CS) and Born-Infeld (BI) in higher dimensions. The occurence of naked singularities are studied and it is found that, the spacetime behaves nonsingular in quantum mechanical sense when it is probed with quantum test particles. The theorem is extended to cover Bertotti-Robinson (BR) type solutions in the presence of the GB parameter alone. Finally we prove also that extension of the theorem for a scalar-tensor source of higher dimensions (N > 4) fails to work.Yayın Gravitational lensing in rotating and twisting universes(Elsevier, 2021) Gürtuğ, Özay; Mangut, Mert; Halilsoy, Mustafa; Gürtuğ, ÖzayGravitational lensing caused by the gravitational field of massive objects has been studied and acknowledged for a long period of time. In this paper, however, we propose a different mechanism where the bending of light stems from the non-linear interaction of gravitational, electromagnetic and axion waves that creates the high curvature zone in the space-time fabric. The striking distinction in the present study is that in contrast to the convex lensing in the gravitational field of a massive object, hyperbolic nature of the high curvature zone of the background space-time may give rise to concave lensing. Expectedly detection of this kind of lensing becomes possible through satellite detectors.Yayın Horizon instability in the cross polarized Bell - Szekeres spacetime(Cornell University, 2000) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayThe quasiregular singularities (horizons) that form in the collision of cross polarized electromagnetic waves are, as in the linear polarized case, unstable. The validity of the Helliwell-Konkowski stability conjecture is tested for a number of exact backreaction cases. In the test electromagnetic case the conjecture fails to predict the correct nature of the singularity while in the scalar field and in the null dust cases the aggrement is justified.Yayın Neutrino fields in a sandwich gravitational wave background(Iop Publishing Ltd, 2022) Dereli, Tekin; Gürtuğ, Özay; Halilsoy, Mustafa; Senikoğlu, YorgoSandwich gravitational waves are given globally in terms of step functions at the boundaries. Linearized Einstein-Weyl equations are solved exactly in this background in Rosen coordinates. Depending on the geometry and composition of the sandwich wave, the neutrino's energy-momentum redistributes itself. At the test field level, since the background will not change, the neutrino's energy density in particular will show variations between positive and negative extrema when crossing the sandwich wave. This may reveal facts about the weakly interacting neutrinos in cosmology.Yayın A new Einstein-nonlinear electrodynamics solution in 2+1-dimensions(Springerlink, 2013) Mazharimousavi, S. Habib; Halilsoy, Mustafa; Gürtuğ, Özay; Gürtuğ, ÖzayWe 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 Fµ? = E0? t µ? ? ? for E0 = constant. First, we show that the metric for zero cosmological constant and the Power-Maxwell Lagrangian of the form of p |Fµ?F µ?|, 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.Yayın New singular and nonsingular colliding wave solutions in Einstein-Maxwell-Scalar theory.(Springerlink, 2003) Gürtuğ, Özay; Halilsoy, Mustafa; Sakallı, İzzet; Gürtuğ, ÖzayA technique is given to generate coupled scalar field solutions in colliding Einstein-Maxwell (EM) waves. By employing the Bell - Szekeres solution as seed and depending on the chosen scalar field, it is possible to construct nonsingular solutions. If the original EM solution is already singular, addition of scalar fields does not make the physics any better. In particular, scalar field solution that is transformable to spherical symmetry is plagued with singularities.Yayın Null singularities in colliding waves(Cornell University, 2001) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayColliding Einstein - Maxwell - Scalar fields need not necessarily doomed to become in a spacelike singularity. Examples are given in which null singularities emerge as intermediate stages between a spacelike singularity and a regular horizon.Yayın Null singularity formation by scalar fields in colliding waves and black holes(Cornell University, 2002) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayIt was believed that when gravitational, electromagnetic and scalar waves interact, a spacelike curvature singularity or Cauchy horizon develops because of mutual focusing. We show with an exact solution that the collision of Einstein-Maxwell-Scalar fields, in contrast to previous studies, predicts singularities on null surfaces and that this is a transition phase between spacelike singularities and regular horizons. Divergences of tidal forces in the null singularities is shown to be weaker relative to the spacelike ones. Using the local isometry between colliding plane waves and black holes, we show that the inner horizon of Reissner-Nordstrom black hole transforms into a null singularity when a particular scalar field is coupled to it. We also present an analytic exact solution, which represents a Reissner-Nordstrom black hole with scalar hair in between the ergosphere.Yayın Probing naked singularities in the charged and uncharged ? - metrics with quantum wave packets(Springer/Plenum Publishers, 2023) Gurtug, Ozay; Halilsoy, Mustafa; Mangut, MertThe non-trivial naked singularities that possess directional behavior in the charged and uncharged Zipoy-Voorhees (ZV) spacetimes, known as ? - metrics are investigated within the context of quantum mechanics. Classically singular spacetime is understood as a geodesic incompleteness with respect to a particle probe, while quantum singularity is understood as a non-unique evolution of test quantum wave packets. In this study, quantum wave packets obeying Klein-Gordon equation are used to probe timelike naked singularities. It is shown by rigorous mathematical calculations that the outermost singularity developed in the charged and uncharged ZV spacetime on the equatorial plane is quantum mechanically singular for all values of the deformation parameter ?. However, directional singularities that develop on the symmetry axis is shown to be healed partially for specific range of the parameter ?, if the analysis is restricted purposely to only specific mode (s-wave mode). Allowing arbitrary modes, classical directional singularities remains quantum singular.Yayın Quantum probes of timelike naked singularities in the weak eld regime of f(R) global monopole spacetime(Springerlink, 2014) Gürtuğ, Özay; Halilsoy, Mustafa; Mazharimousavi, S. Habib; Gürtuğ, ÖzayThe formation of a naked singularity in f(R) global monopole spacetime is considered in view of quantum mechanics. Quantum test elds 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 elds 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 elds having di erent 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 speci c modes electromagnetic (spin 1) and Dirac eld (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.Yayın Reflection of electromagnetic waves from mixtures of plane gravitational and scalar waves(APS Physics, 2006) Gürtuğ, Özay; Halilsoy, Mustafa; Ünver, Özlem; Gürtuğ, ÖzayWe consider colliding wave packets consisting of hybrid mixtures of electromagnetic, gravitational and scalar waves. Irrespective of the scalar field, the electromagnetic wave still reflects from the gravitational wave. Some reflection processes are given for different choice of packets in which the Coulomb-like component ? 2 vanishes. Exact solution for multiple reflection of an electromagnetic wave from successive impulsive gravitational waves is obtained in a closed form. It is shown that a succesive sign flip in the Maxwell spinor arises as a result of encountering with an impulsive train ( i.e. the Dirac’s comb curvature) of gravitational waves. Such an observable effect may be helpful in the detection of gravitational wave bursts.Yayın Restricted class of colliding Einstein-Yang-Mills plane waves(WorldScientific, 2009) Gürtuğ, Özay; Halilsoy, Mustafa; Gürtuğ, ÖzayBy gauging an Abelian electromagnetic (em) solution through a non-Abelian transformation and in accordance with a theorem proved long time ago, we construct a simple class of colliding Einstein-Yang-Mills (EYM) plane waves. The solution is isometric to the Wu-Yang charged KerrNewman (KN) black hole and shares much of the properties satisfied by colliding Einstein-Maxwell (EM) plane waves. In the linear polarization limit with unit degenerate charge it reduces to the Bell-Szekeres (BS) solution for colliding em shock waves.Yayın Rindler modified schwarzschild geodesics(Springerlink, 2013) Halilsoy, Mustafa; Gürtuğ, Özay; Mazharimousavi, S. Habib; Gürtuğ, ÖzayThe 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.Yayın Search for gravitational waves through the electromagnetic faraday rotation(APS Physics, 2007) Halilsoy, Mustafa; Gürtuğ, Özay; Gürtuğ, ÖzayA method is given which renders indirect detection of strong gravitational waves possible. This is based on the reflection (collision) of a linearly polarized electromagnetic shock wave from (with) a cross polarized impulsive and shock gravitational waves in accordance with the general theory of relativity. This highly non-linear process induces a detectable Faraday rotation in the polarization vector of the electromagnetic field.
