Browsing by Author "Tekin, B."
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Item Open Access AdS waves as exact solutions to quadratic gravity(American Physical Society, 2011-04-08) Güllü, I.; Gürses, M.; Sişman, T.C.; Tekin, B.We give an exact solution of the quadratic gravity in D dimensions. The solution is a plane-fronted wave metric with a cosmological constant. This metric solves not only the full quadratic gravity field equations but also the linearized ones which include the linearized equations of the recently found critical gravity. A subset of the solutions change the asymptotic structure of the anti-de Sitter space due to their logarithmic behavior. © 2011 American Physical Society.Item Open Access AdS-Plane wave and pp-wave solutions of generic gravity theories(American Physical Society, 2014-12-02) Gürses M.; Şişman, T. Ç.; Tekin, B.We construct the anti–de Sitter-plane wave solutions of generic gravity theory built on the arbitrary powers of the Riemann tensor and its derivatives in analogy with the pp-wave solutions. In constructing the wave solutions of the generic theory, we show that the most general two-tensor built from the Riemann tensor and its derivatives can be written in terms of the traceless Ricci tensor. Quadratic gravity theory plays a major role; therefore, we revisit the wave solutions in this theory. As examples of our general formalism, we work out the six-dimensional conformal gravity and its nonconformal deformation as well as the tricritical gravity, the Lanczos-Lovelock theory, and string-generated cubic curvature theory.Item Open Access Anti-de sitter-wave solutions of higher derivative theories(American Physical Society, 2013) Gürses, M.; Hervik, S.; Şişman, T. Ç.; Tekin, B.We show that the recently found anti-de Sitter (AdS)-plane and AdS-spherical wave solutions of quadratic curvature gravity also solve the most general higher derivative theory in D dimensions. More generally, we show that the field equations of such theories reduce to an equation linear in the Ricci tensor for Kerr-Schild spacetimes having type-N Weyl and type-N traceless Ricci tensors. © 2013 American Physical Society.Item Open Access Classical double copy: Kerr-Schild-Kundt metrics from Yang-Mills theory(American Physical Society, 2018) Gürses, Metin; Tekin, B.The classical double copy idea relates some solutions of Einstein's theory with those of gauge and scalar field theories. We study the Kerr-Schild-Kundt (KSK) class of metrics in d dimensions in the context of possible new examples of this idea. We first show that it is possible to solve the Einstein-Yang-Mills system exactly using the solutions of a Klein-Gordon-type scalar equation when the metric is the pp-wave metric, which is the simplest member of the KSK class. In the more general KSK class, the solutions of a scalar equation also solve the Yang-Mills, Maxwell, and Einstein-Yang-Mills-Maxwell equations exactly, albeit with a null fluid source. Hence, in the general KSK class, the double copy correspondence is not as clear-cut as in the case of the pp wave. In our treatment, all the gauge fields couple to dynamical gravity and are not treated as test fields. We also briefly study Gödel-type metrics along the same lines.Item Open Access Comment on “Einstein-Gauss-Bonnet Gravity in four-dimensional spacetime”(American Physical Society, 2020) Gürses, Metin; Şişman, T. Ç.; Tekin, B.We summarize our proof that the "Einstein-Gauss-Bonnet Gravity in Four-Dimensional Spacetime" introduced in Phys. Rev. Lett. 124, 081301 (2020) does not have consistent field equations, as such the theory does not exist. The proof is given in both the metric and the first order formalisms.Item Open Access From smooth curves to universal metrics(American Physical Society, 2016) Gürses M.; Şişman, T.Ç.; Tekin, B.A special class of metrics, called universal metrics, solves all gravity theories defined by covariant field equations purely based on the metric tensor. Since we currently lack the knowledge of what the full quantum-corrected field equations of gravity are at a given microscopic length scale, these metrics are particularly important in understanding quantum fields in curved backgrounds in a consistent way. However, finding explicit universal metrics has been a difficult problem as there does not seem to be a procedure for it. In this work, we overcome this difficulty and give a construction of universal metrics of d-dimensional spacetime from curves constrained to live in a (d-1)-dimensional Minkowski spacetime or a Euclidean space. © 2016 American Physical Society.Item Open Access Gravity waves in three dimensions(American Physical Society, 2015) Gürses, M.; Şişman, T. Ç.; Tekin, B.We find the explicit forms of the anti-de Sitter plane, anti-de Sitter spherical, and pp waves that solve both the linearized and exact field equations of the most general higher derivative gravity theory in three dimensions. As a subclass, we work out the six-derivative theory and the critical version of it where the masses of the two spin-2 excitations vanish and the spin-0 excitations decouple. © 2015 American Physical Society.Item Open Access Is there a novel Einstein–Gauss–Bonnet theory in four dimensions?(Springer, 2020-07) Gürses, Metin; Şişman, T. Ç.; Tekin, B.No! We show that the field equations of Einstein–Gauss–Bonnet theory defined in generic D>4D>4 dimensions split into two parts one of which always remains higher dimensional, and hence the theory does not have a non-trivial limit to D=4D=4. Therefore, the recently introduced four-dimensional, novel, Einstein–Gauss–Bonnet theory does not admit an intrinsically four-dimensional definition, in terms of metric only, as such it does not exist in four dimensions. The solutions (the spacetime, the metric) always remain D>4D>4 dimensional. As there is no canonical choice of 4 spacetime dimensions out of D dimensions for generic metrics, the theory is not well defined in four dimensions.Item Open Access Israel-Wilson-Perjes metrics in a theory with a dilaton field(American Physical Society, 2023-07-25) Gürses, Metin; Şişman, T. Ç.; Tekin, B.We are interested in the charged dust solutions of the Einstein field equations in stationary and axially symmetric spacetimes and inquire if the naked singularities of the Israel-Wilson-Perjes (IWP) metrics can be removed. The answer is negative in four dimensions. We examine whether this negative result can be avoided by adding scalar or dilaton fields. We show that IWP metrics also arise as solutions of the Einstein-Maxwell system with a stealth dilaton field. We determine the IWP metrics completely in terms of one complex function satisfying the Laplace equation. With the inclusion of the stealth dilaton field, it is now possible to add a perfect fluid source. In this case, the field equations reduce to a complex cubic equation. Hence, this procedure provides interior solutions to each IWP metric, and it is possible to cover all naked singularities inside a compact surface where there is matter distribution.Item Open Access Kerr-Schild–Kundt metrics are universal(Institute of Physics Publishing, 2017) Gürses M.; Şişman, T. Ç.; Tekin, B.We define (non-Einsteinian) universal metrics as the metrics that solve the source-free covariant field equations of generic gravity theories. Here, extending the rather scarce family of universal metrics known in the literature, we show that the Kerr-Schild-Kundt class of metrics are universal. Besides being interesting on their own, these metrics can provide consistent backgrounds for quantum field theory at extremely high energies. © 2017 IOP Publishing Ltd.Item Open Access New exact solutions of quadratic curvature gravity(American Physical Society, 2012) Gürses, M.; Şişman, T. Ç.; Tekin, B.It is a known fact that the Kerr-Schild type solutions in general relativity satisfy both exact and linearized Einstein field equations. We show that this property remains valid also for a special class of the Kerr-Schild metrics in arbitrary dimensions in generic quadratic curvature theory. In addition to the anti-de Sitter (AdS) wave (or Siklos) metric which represents plane waves in an AdS background, we present here a new exact solution, in this class, to the quadratic gravity in D dimensions which represents a spherical wave in an AdS background. The solution is a special case of the Kundt metrics belonging to spacetimes with constant curvature invariants. © 2012 American Physical Society.Item Open Access Non-Einsteinian black holes in generic 3D gravity theories(American Physical Society, 2019) Gürses, Metin; Şişman, T. Ç.; Tekin, B.The Bañados-Teitelboim-Zanelli (BTZ) black hole metric solves the three-dimensional Einstein’s theory with a negative cosmological constant as well as all the generic higher derivative gravity theories based on the metric; as such it is a universal solution. Here, we find, in all generic higher derivative gravity theories, new universal non-Einsteinian solutions obtained as Kerr-Schild type deformations of the BTZ black hole. Among these, the deformed nonextremal BTZ black hole loses its event horizon while the deformed extremal one remains intact as a black hole in any generic gravity theory.Item Open Access Some exact solutions of all f (R μν) theories in three dimensions(American Physical Society, 2012) Gürses, M.; Şişman, T. Ç.; Tekin, B.We find constant scalar curvature Type-N and Type-D solutions in all higher curvature gravity theories with actions of the form f(R μν) that are built on the Ricci tensor, but not on its derivatives. In our construction, these higher derivative theories inherit some of the previously studied solutions of the cosmological topologically massive gravity and the new massive gravity field equations, once the parameters of the theories are adjusted. Besides the generic higher curvature theory, we have considered in some detail the examples of the quadratic curvature theory, the cubic curvature theory, and the Born-Infeld extension of the new massive gravity. © 2012 American Physical Society.Item Open Access Superposition of FLRW universes(Institute of Physics Publishing, 2020) Gürses, Metin; Yaghoub, Heydarzade; Tekin, B.We show that (1) the Einstein field equations with a perfect fluid source admit a nonlinear superposition of two distinct homogenous Friedman-Lemaitre-Robertson-Walker (FLRW) metrics as a solution, (2) the superposed solution is an inhomogeneous geometry in general, (3) it reduces to a homogeneous one in the two asymptotes which are the early and the late stages of the universe as described by two different FLRW metrics, (4) the solution possesses a scale factor inversion symmetry and (5) the solution implies two kinds of topology changes: one during the time evolution of the superposed universe and the other occurring in the asymptotic region of space.