Person: DELİCE, ÖZGÜR
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DELİCE
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ÖZGÜR
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Publication Metadata only On generalized Einstein-Rosen waves in Brans-Dicke theory(SPRINGER HEIDELBERG, 2014) DELİCE, ÖZGÜR; Akyar, Lokman; Delice, OzgurIn this paper cylindrically symmetric vacuum solutions corresponding to generalized Einstein-Rosen-type gravitational waves are considered in the framework of Brans-Dicke (BD) scalar-tensor theory. We see that, similar to axially symmetric vacuum solutions, under some assumptions, it is possible to generate BD-vacuum solutions from corresponding solutions in general relativity. Using this generating technique, we present several exact solutions corresponding to soliton, standing or pulse waves in BD theory. We also present a Kasner-type time-dependent generalization of cylindrically symmetric static vacuum solution. Some physical implications of these solutions are discussed in some detail. The effect of pulse type waves on test particle motion is briefly discussed and compared with static vacuum background. We also see that, similar to general relativity, there are no trapped cylinders in Einstein-Rosen-type solutions in BD theory.Publication Metadata only Static Weyl Type Solutions of The Brans-Dicke Theory(AMER INST PHYSICS, 2016) DELİCE, ÖZGÜR; Kirezli, Pinar; Delice, Ozgur; Akkus, B; Oktem, Y; Yalcin, LS; Mutlu, RBC; Dogan, GSStatic, axially symmetric Weyl type solutions and their properties are studied in the Brans-Dicke (BD) theory. The new solutions are obtained for the general Weyl solutions, two particle Chazy-Curzon solution and Bertotti-Robinson type solution. Some physical properties such as the geodesic motion and singularities of these solutions are also discussed in detail.Publication Open Access Superradiance of a global monopole in Reissner-Nordstrom(-AdS) space-time(SPRINGER, 2020-05) SEÇUK, MUHAMMED HALUK; Secuk, M. Haluk; Delice, OzgurIn this article, the behavior of a charged and massive scalar field around a global monopole swallowed by a Reissner-Nordstrom-Anti-de Sitter (RN-AdS) black hole is investigated by considering the Klein-Gordon equation in this geometry. The superradiance phenomenon and instability behavior of the black hole against charged scalar perturbations are studied for both an RN-AdS case and also for an RN black hole surrounded by a reflective mirror, i.e., the black hole bomb case. The effects of the monopole on these cases are discussed analytically and also with the help of several graphs in detail. The monopole charge affects the superradiance threshold frequency and also effects the instability time scale for both cases. The existence of global monopole makes these black holes more stable against superradiance instability.Publication Open Access Linearized modified gravity theories with a cosmological term: advance of perihelion and deflection of light(IOP PUBLISHING LTD, 2018-03-22) DELİCE, ÖZGÜR; Ozer, Hatice; Delice, OzgurTwo different ways of generalizing Einstein's general theory of relativity with a cosmological constant to Brans-Dicke type scalar-tensor theories are investigated in the linearized field approximation. In the first case a cosmological constant term is coupled to a scalar field linearly whereas in the second case an arbitrary potential plays the role of a variable cosmological term. We see that the former configuration leads to a massless scalar field whereas the latter leads to a massive scalar field. General solutions of these linearized field equations for both cases are obtained corresponding to a static point mass. Geodesics of these solutions are also presented and solar system effects such as the advance of the perihelion, deflection of light rays and gravitational redshift were discussed. In general relativity a cosmological constant has no role in these phenomena. We see that for the Brans-Dicke theory, the cosmological constant also has no effect on these phenomena. This is because solar system observations require very large values of the Brans-Dicke parameter and the correction terms to these phenomena becomes identical to GR for these large values of this parameter. This result is also observed for the theory with arbitrary potential if the mass of the scalar field is very light. For a very heavy scalar field, however, there is no such limit on the value of this parameter and there are ranges of this parameter where these contributions may become relevant in these scales. Galactic and intergalactic dynamics is also discussed for these theories at the latter part of the paper with similar conclusions.Publication Open Access Generalized Sparling-Thirring form in the Brans-Dicke theory(SPRINGER, 2015-02) DELİCE, ÖZGÜR; Baykal, Ahmet; Delice, OzgurThe definition of the Sparling-Thirring form is extended to Brans-Dicke theory. By writing the Brans-Dicke field equations in a formally Maxwell-like form, a superpotential and a corresponding pseudo-energy-momentum form are defined. The general energy expression provided by the superpotential in the Jordan frame is discussed in relation to the corresponding expression in the Einstein frame. In order to substantiate its formal definition, the generalized Sparling-Thirring form is used to calculate the energy for the spherically symmetric vacuum solution in Brans-Dicke theory.Publication Open Access Gravitational waves in Brans-Dicke theory with a cosmological constant(SPRINGER, 2021-04) DELİCE, ÖZGÜR; Ozer, Hatice; Delice, OzgurWeak field gravitational wave solutions are investigated in Brans-Dicke (BD) theory in the presence of a cosmological constant. In this setting the background geometry is not flat but asymptotically de-Sitter. We investigate the linearised field equations, and their gravitational wave solutions in a certain gauge choice. We will show that this theory leads to massless scalar waves as in original BD theory and in contrast to massive BD theory. The effects of these waves on free particles and their polarization properties are studied extensively and effects of the cosmological constant is analyzed in these phenomena in detail. The energy flux of these waves are also discussed in this background. By analyzing this flux, we obtain a critical distance where the waves cannot propagate further, which extends Cosmic no Hair Conjecture (CNC) to BD theory with a cosmological constant.Publication Open Access Higher dimensional cylindrical or Kasner type electrovacuum solutions(SPRINGER/PLENUM PUBLISHERS, 2013-11) DELİCE, ÖZGÜR; Delice, Ozgur; Kirezli, Pinar; Ciftci, Dilek K.We consider a dimensional Kasner type diagonal spacetime where metric functions depend only on a single coordinate and electromagnetic field shares the symmetries of spacetime. These solutions can describe static cylindrical or cosmological Einstein-Maxwell vacuum spacetimes. We mainly focus on electrovacuum solutions and four different types of solutions are obtained in which one of them has no four dimensional counterpart. We also consider the properties of the general solution corresponding to the exterior field of a charged line mass and discuss its several properties. Although it resembles the same form with four dimensional one, there is a difference on the range of the solutions for fixed signs of the parameters. General magnetic field vacuum solution are also briefly discussed, which reduces to Bonnor-Melvin magnetic universe for a special choice of the parameters. The Kasner forms of the general solution are also presented for the cylindrical or cosmological cases.Publication Open Access Brans-Dicke-Maxwell solutions for higher dimensional static cylindrical symmetric spacetime(AMER INST PHYSICS, 2015-07) DELİCE, ÖZGÜR; Ciftci, Dilek K.; Delice, OzgurIn this paper, Brans-Dicke-Maxwell type vacuum solutions are considered for a static cylindrically symmetric spacetime in arbitrary dimensions. Exact solutions are obtained by directly solving the field equations for the case where an azimuthal magnetic field is present. Other configurations such as axial magnetic field case can be obtained by suitably relabeling the coordinates. We have also considered conformally related Einstein frame to relate the solutions we have obtained with the dilaton-Maxwell type solutions that exist in the literature. We see that for a special case the general solution we present reduces to dilaton-Melvin spacetime. The general relativistic limit of these solutions is also discussed and we found that this limit is different from the four dimensional case. (C) 2015 AIP Publishing LLC.Publication Open Access A unified approach to variational derivatives of modified gravitational actions(IOP PUBLISHING LTD, 2011-01-07) DELİCE, ÖZGÜR; Baykal, Ahmet; Delice, OZgurOur main aim in this paper is to promote the coframe variational method as a unified approach to derive field equations for any given gravitational action containing the algebraic functions of the scalars constructed from the Riemann curvature tensor and its contractions. We are able to derive a master equation which expresses the variational derivatives of the generalized gravitational actions in terms of the variational derivatives of its constituent curvature scalars. Using the Lagrange multiplier method relative to an orthonormal coframe, we investigate the variational procedures for modified gravitational Lagrangian densities in spacetime dimensions n >= 3. We study the well-known gravitational actions such as those involving the Gauss-Bonnet and Ricci-squared, Kretchmann scalar, Weyl-squared terms and their algebraic generalizations similar to generic f(R) theories and the algebraic generalization of sixth order gravitational Lagrangians. We put forth a new model involving the gravitational Chern-Simons term and also give three-dimensional new massive gravity equations in a new form in terms of the Cotton 2-form.Publication Metadata only Some Properties of Magnetized Bonnor-Dihole Solution in Brans-Dicke Theory(AMER INST PHYSICS, 2017) DELİCE, ÖZGÜR; Kirezli, Pinar; Delice, Ozgur; Akkus, B; Oktem, Y; Dogan, GS; Guzelcimen, FSoule properties of magnetized Bonnor-dihole solution in Brans Dicke(BD) theory is discussed. Conical deficit angle and equatiorial geodesics of (jawlike and null particles are investigated in detail for different values of the parameters of the BD solution.