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A class of 4-dimensional supersymmetric dyonic black hole solutions that arise in an effective 11-dimensional supergravity compactified on a 7-torus is presented. We give the explicit form of dyonic solutions with diagonal internal metric,…
An internal singularity of a string four-dimensional black hole with second order curvature corrections is discussed. A restriction to a minimal size of a neutral black hole is obtained in the frame of the model considered. Vacuum…
In this article, we consider a class of four-dimensional Einstein-Maxwell theory which is coupled non-minimally to a scalar field and the Gauss-Bonnet invariant. We mainly use the numerical methods to find the solutions to the theory, with…
We examine an exact solution which represents a charged black hole in a Kaluza-Klein universe in the five-dimensional Einstein-Maxwell theory. The spacetime approaches to the five-dimensional Kasner solution that describes expanding three…
We introduce the Liouville mode into the Green-Schwarz superstring. Like massive supersymmetry without central charges, there is no kappa symmetry. However, the second-class constraints (and corresponding Wess-Zumino term) remain, and can…
We identify a string theory counterpart of the dilatonic Melvin D=4 background describing a "magnetic flux tube" in low-energy field theory limit. The corresponding D=5 bosonic string model containing extra compact Kaluza-Klein dimension is…
One of the leading candidates for quantum gravity, viz. string theory, has the following features incorporated in it. (i) The full spacetime is higher dimensional, with (possibly) compact extra-dimensions; (ii) There is a natural minimal…
In Kaluza-Klein theory, gauge fields on $M_4$ arise as components of a higher-dimensional metric defined on $M_4 \times K$. The traditional expectation is that all the gauge fields of the Standard Model are linked to exact Killing vector…
A new 5-dimensional Classical Unified Field Theory of Kaluza-Klein type is formulated using 2 separate scalar fields which are related in such a way as to make the 5-dimensional matter-geometry coupling parameter constant. It is shown that…
We formulate four dimensional higher spin gauge theories in spacetimes with signature (4-p,p) and nonvanishing cosmological constant. Among them are chiral models in Euclidean (4,0) and Kleinian (2,2) signature involving half-flat gauge…
Global properties of static, spherically symmetric configurations of scalar fields of sigma-model type with arbitrary potentials are studied in $D$ dimensions, including space-times containing multiple internal factor spaces. The latter are…
A geometrical model of electric charge is proposed. This model has ``naked'' charge screened with a ``fur - coat'' consisting of virtual wormholes. The 5D wormhole solution in the Kaluza - Klein theory is the ``naked'' charge. The splitting…
We study four-dimensional gravity theories that are rendered renormalisable by the inclusion of curvature-squared terms to the usual Einstein action with cosmological constant. By choosing the parameters appropriately, the massive scalar…
The unimodular version of the Kaluza-Klein theory is briefly recalled, and its projection on the $4$-dimensional spacetime is constructed. Imposing unimodularity condition on the $5$-dimensional Kaluza-Klein metric, det$g_{AB}=1$ is…
We construct new 1/2 supersymmetric solutions in D=3, N=2, matter coupled, U(1) gauged supergravities and study some of their properties. In the most general case they represent a string superposed with gravitational and Chern-Simons…
A free superstring with chiral N=2 supersymmetry in six dimensions is proposed. It couples to a two-form gauge field with a self-dual field strength. Compactification to four dimensions on a two-torus gives a strongly coupled N=4…
In six dimensions there exists a unique one-parameter family of non-linear conformal electrodynamics for a chiral 2-form gauge field which includes (in a free-field limit) the linear chiral 2-form theory and is related, by dimensional…
We derive extremal black hole solutions for a variety of four dimensional models which, after Kaluza-Klein reduction, admit a description in terms of 3D gravity coupled to a sigma model with symmetric target space. The solutions are in…
Gravitational waves with a space-translation Killing field are considered. In this case, the 4-dimensional Einstein vacuum equations are equivalent to the 3-dimensional Einstein equations with certain matter sources. This interplay between…
We study four dimensional field theory from the low-energy effective theory of Type I, II or heterotic string theories. Chiral fermions in four dimensions are obtained by several mechanisms. Especially, the background flux is one of the…