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Permanent URI for this collectionhttps://acikarsiv.thk.edu.tr/handle/123456789/2550
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Publication Is there a novel Einstein–Gauss–Bonnet theory in four dimensions?(Springer Science and Business Media LLC, 2020-07) Metin Gürses; Tahsin Çağrı Şişman; Bayram TekinAbstractNo! We show that the field equations of Einstein–Gauss–Bonnet theory defined in generic $$D>4$$D>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 $$D=4$$D=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 $$D>4$$D>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.Publication Comment on “Einstein-Gauss-Bonnet Gravity in Four-Dimensional Spacetime”(American Physical Society (APS), 2020-09-28) Metin Gürses; Tahsin Çağrı Şişman; Bayram TekinPublication Kerr–Schild–Kundt metrics in generic gravity theories with modified Horndeski couplings(Springer Science and Business Media LLC, 2021-12) Metin Gürses; Yaghoub Heydarzade; Çetin Şentürk; Şentürk, Çetin; Şentürk, Çetin; Şentürk, ÇetinAbstractThe Kerr–Schild–Kundt (KSK) metrics are known to be one of the universal metrics in general relativity, which means that they solve the vacuum field equations of any gravity theory constructed from the curvature tensor and its higher-order covariant derivatives. There is yet no complete proof that these metrics are universal in the presence of matter fields such as electromagnetic and/or scalar fields. In order to get some insight into what happens when we extend the “universality theorem” to the case in which the electromagnetic field is present, as a first step, we study the KSK class of metrics in the context of modified Horndeski theories with Maxwell’s field. We obtain exact solutions of these theories representing the pp-waves and AdS-plane waves in arbitrary D dimensions.Publication Kerr-Schild-Kundt metrics in generic Einstein-Maxwell theories(American Physical Society (APS), 2022-02-03) Metin Gürses; Yaghoub Heydarzade; Çetin Şentürk; Şentürk, Çetin; Şentürk, Çetin; Şentürk, ÇetinPublication Israel-Wilson-Perjes metrics in a theory with a dilaton field(American Physical Society (APS), 2023-07-25) Metin Gürses; Tahsin Çaǧrı Şişman; Bayram Tekin