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Bayram Tekin

Publications and source records attributed to Bayram Tekin.

At least 127 records · Page 7Linked to original sources
arXiv2009

Green's Matrix for a Second Order Self-Adjoint Matrix Differential Operator

A systematic construction of the Green's matrix for a second order, self-adjoint matrix differential operator from the linearly independent solutions of the corresponding homogeneous differential equation set is carried out. We follow the general approach of extracting the Green's matrix from the Green's matrix of the corresponding first order system. This construction is required in the cases where the differential equation set cannot be turned to an algebraic equation set via transform techniques.

math-ph↗
arXiv2009

Self-dual solutions of Yang-Mills theory on Euclidean AdS space

We find non-trivial, time-dependent solutions of the (anti) self-dual Yang-Mills equations in the four dimensional Euclidean Anti-de Sitter space. In contrast to the Euclidean flat space, the action depends on the moduli parameters and the charge can take any non-integer value.

hep-th↗
arXiv2008

Comment on the new AdS universe

We show that Bonnor's new Anti-de Sitter (AdS) universe and its D-dimensional generalization is the previously studied AdS soliton.

gr-qc↗
arXiv2008

Finite mass gravitating Yang monopoles

We show that gravity cures the infra-red divergence of the Yang monopole when a proper definition of conserved quantities in curved backgrounds is used, i.e. the gravitating Yang monopole in cosmological Einstein theory has a finite mass in generic even dimensions (including time). In addition, we find exact Yang-monopole type solutions in the cosmological Einstein-Gauss-Bonnet-Yang-Mills theory and briefly discuss their properties.

hep-th↗
arXiv2008

Cotton flow

Using the conformally invariant Cotton tensor, we define a geometric flow, the "Cotton flow", which is exclusive to three dimensions. This flow tends to evolve the initial metrics into conformally flat ones, and is somewhat orthogonal to the Yamabe flow, the latter being a flow within a conformal class. We define an entropy functional, and study the flow of nine homogeneous spaces both numerically and analytically. In particular, we show that the arbitrarily deformed homogeneous 3-sphere flows into the round 3-sphere. Two of the nine homogeneous geometries, which are degenerated by the Ricci flow, are left intact by the Cotton flow.

hep-th↗
arXiv2008

Another proof of the positive energy theorem in gravity

We show that gravitational energy expression simplifies when a new set of coordinates that satisfies a certain asymptotic gauge condition is used. Compared to the ADM formula, positivity of the energy is more transparent in this new construction. Our proof relies on the asymptotic symmetries (specifically supertranslations) of the asymptotically flat spacetimes at spatial infinity in four dimensions.

gr-qc↗
arXiv2008

Impact of Casimir Force in Molecular Electronic Switching Junctions

Despite significant progress in synthesizing several new molecules and many promising single device demonstrations, wide range acceptance of molecular electronics as an alternative to CMOS technology has been stalled not only by controversial theories of a molecular device`s operation, for example the switching mechanism, but also by our inability to reproducibly fabricate large arrays of devices. In this paper, we investigate the role of Casimir force as one of the potential source of a wide range of discrepancies in the reported electrical characteristics and high rate of device shorting in molecular electronic switching junctions fabricated by sandwiching a molecular monolayer between a pair of planar metal electrode.

cond-mat.mtrl-sci↗
arXiv2007

Chern-Simons Modified General Relativity: Conserved charges

We construct the conserved charges (mass and angular momentum) of the Chern-Simons modified General Relativity in asymptotically flat and Anti-de Sitter (AdS) spacetimes. Our definition is based on background Killing symmetries and reduces to the known expressions in the proper limits.

gr-qc↗
arXiv2007

New Energy Definition for Higher Curvature Gravities

We propose a novel but natural definition of conserved quantities for gravity models quadratic and higher in curvature. Based on the spatial asymptotics of curvature rather than of metric, it avoids the GR energy machinery's more egregious problems--such as zero energy "theorems" and failure in flat backgrounds -- in this fourth-derivative realm. In D>4, the present expression indeed correctly discriminates between second derivative Gauss-Bonnet and generic, fourth derivative, actions.

gr-qc↗
arXiv2006

Gravitational charges of transverse asymptotically AdS spacetimes

Using Killing-Yano symmetries, we construct conserved charges of spacetimes that asymptotically approach to the flat or Anti-de Sitter spaces only in certain directions. In D dimensions, this allows one to define gravitational charges (such as mass and angular momenta densities) of p-dimensional branes/solitons or any other extended objects that curve the transverse space into an asymptotically flat or AdS one. Our construction answers the question of what kind of charges the antisymmetric Killing-Yano tensors lead to.

hep-th↗
arXiv2006

Topologically massive gravity as a Pais-Uhlenbeck oscillator

We give a detailed account of the free field spectrum and the Newtonian limit of the linearized "massive" (Pauli-Fierz), "topologically massive" (Einstein-Hilbert-Chern-Simons) gravity in 2+1 dimensions about a Minkowski spacetime. For a certain ratio of the parameters, the linearized free theory is Jordan-diagonalizable and reduces to a degenerate "Pais-Uhlenbeck" oscillator which, despite being a higher derivative theory, is ghost-free.

gr-qc↗
arXiv2006

Conformal Properties of Charges in Scalar-Tensor Gravities

We study the behavior under conformal transformations of energy and other charges in generic scalar-tensor models. This enables us to conclude that the ADM/AD masses are invariant under field redefinitions mixing metric and scalar despite the permitted slow asymptotic falloff of massless scalars.

gr-qc↗
arXiv2006

Negative Mass Solitons in Gravity

We first reconstruct the conserved (Abbott-Deser) charges in the spin connection formalism of gravity for asymptotically (Anti)-de Sitter spaces, and then compute the masses of the AdS soliton and the recently found Eguchi-Hanson solitons in generic odd dimensions, unlike the previous result obtained for only five dimensions. These solutions have negative masses compared to the global AdS or AdS/Z_p spacetimes. As a separate note, we also compute the masses of the recent even dimensional Taub-NUT-Reissner-Nordstrom metrics.

hep-th↗
arXiv2003

Energy in Topologically Massive Gravity

We define conserved gravitational charges in -cosmologically extended- topologically massive gravity, exhibit them in surface integral form about their de-Sitter or flat vacua and verify their correctness in terms of two basic types of solution.

gr-qc↗
arXiv2003

Kaluza-Klein Monopole in AdS Spacetime

We construct analogs of the flat space Kaluza-Klein (KK) monopoles in locally Anti-de Sitter (AdS) spaces for $D \ge 5+1$. We show that, unlike the flat space KK monopole, there is no five dimensional static KK monopole in AdS that smoothly reduces to the flat space one as the cosmological constant goes to zero. Thus, one needs at least two extra dimensions, one of which is compact, to get a static KK monopole in cosmological backgrounds.

hep-th↗