Browsing by Subject "Warped products"
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Item Open Access Characterizing killing vector fields of standard static space-times(Elsevier, 2012) Dobarro, F.; Ünal, B.We provide a global characterization of the Killing vector fields of a standard static space-time by a system of partial differential equations. By studying this system, we determine all the Killing vector fields in the same framework when the Riemannian part is compact. Furthermore, we deal with the characterization of Killing vector fields with zero curl on a standard static space-time. © 2011 Elsevier B.V..Item Open Access Curvature in special base conformal warped products(Springer Netherlands, 2008) Dobarro F.; Ünal, B.We introduce the concept of a base conformal warped product of two pseudo-Riemannian manifolds. We also define a subclass of this structure called as a special base conformal warped product. After, we explicitly mention many of the relevant fields where metrics of these forms and also considerations about their curvature related properties play important rolls. Among others, we cite general relativity, extra-dimension, string and super-gravity theories as physical subjects and also the study of the spectrum of Laplace-Beltrami operators on p-forms in global analysis. Then, we give expressions for the Ricci tensor and scalar curvature of a base conformal warped product in terms of Ricci tensors and scalar curvatures of its base and fiber, respectively. Furthermore, we introduce specific identities verified by particular families of, either scalar or tensorial, nonlinear differential operators on pseudo-Riemannian manifolds. The latter allow us to obtain new interesting expressions for the Ricci tensor and scalar curvature of a special base conformal warped product and it turns out that not only the expressions but also the analytical approach used are interesting from the physical, geometrical and analytical point of view. Finally, we analyze, investigate and characterize possible solutions for the conformal and warping factors of a special base conformal warped product, which guarantee that the corresponding product is Einstein. Besides all, we apply these results to a generalization of the Schwarzschild metric. © 2008 Springer Science+Business Media B.V.Item Open Access Implications of energy conditions on standard static space-times(Pergamon Press, 2009) Dobarro, F.; Ünal, B.In the framework of standard static space-times, we state a family of sufficient or necessary conditions for a set of physically reasonable energy and convergence conditions in relativity and related theories. We concentrate our study on questions about the sub-harmonicity of the warping function, the scalar curvature map, conformal hyperbolicity, conjugate points and the time-like diameter of this class of space-times. © 2009 Elsevier Ltd. All rights reserved.Item Open Access Jacobi vector fields and conjugate points on warped product manifolds(Elsevier Ltd, 2023-06) Dirmeier, Alexander; Scherfner, Mike; Shenawy, Sameh; Ünal, BülentIn this paper, the structure of Jacobi vector fields on warped product manifolds is investigated. Many characterizations of Jacobi vector fields on warped product manifolds are obtained. Consequently, conjugate points on warped product manifolds are also considered. Finally, we apply our results to characterize conjugate points of some well-known warped product spacetimes.