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DELİCE, ÖZGÜR

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DELİCE

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2011 - 201922020 - 20212
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Author: DELİCE, ÖZGÜR × Subject: FIELD ×

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Now showing 1 - 4 of 4
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    PublicationOpen 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, Ozgur
    Two 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.
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    PublicationOpen Access
    Gravitational waves in Brans-Dicke theory with a cosmological constant
    (SPRINGER, 2021-04) DELİCE, ÖZGÜR; Ozer, Hatice; Delice, Ozgur
    Weak 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.
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    PublicationOpen Access
    A unified approach to variational derivatives of modified gravitational actions
    (IOP PUBLISHING LTD, 2011-01-07) DELİCE, ÖZGÜR; Baykal, Ahmet; Delice, OZgur
    Our 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.
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    PublicationOpen Access
    Bending of light from Reissner-Nordstrom-de Sitter-monopole black hole
    (SPRINGER HEIDELBERG, 2020-07) SEÇUK, MUHAMMED HALUK; Secuk, M. Haluk; Delice, Ozgur
    We study light deflection from a Reissner-Nordstrom-de Sitter black hole in the gravitational monopole background. We first calculate the orbit equation and the contribution of the monopole and black hole parameters to the deflection angle up to second order for the vanishing cosmological constant case using the Rindler-Ishak method. We also obtain the contribution of the cosmological constant to light deflection in this geometry in the weak field limit using the same method.