Letter: Gödel-Type Space-Time Metrics

A simple group theoretic derivation is given of the family of space-time metrics with isometry group SO(2,1) × SO(2) × first described by Gödel, of which the Gödel stationary cosmological solution is the member with a perfect-fluid stress-energy tensor. Other members of the family are shown to be interpretable as cosmological solutions with an electrically charged perfect fluid and a magnetic field.     

Linear Perturbations of Hyperkähler Metrics

We study general linear perturbations of a class of 4d real-dimensional hyperkähler manifolds obtainable by the (generalized) Legendre transform method. Using twistor methods, we show that deformations can be encoded in a set of holomorphic functions of 2d + 1 variables, as opposed to the functions of d + 1 variables controlling the unperturbed metric. Such deformations generically break all tri-holomorphic isometries of the unperturbed metric. Geometrically, these functions generate the symplectomorphisms which relate local complex Darboux coordinate systems in different patches of the twistor space. The deformed Kähler potential follows from these data by a Penrose-type transform. As an illustration of our general framework, we determine the leading exponential deviation of the Atiyah–Hitchin manifold away from its negative mass Taub-NUT limit.     

Deformation of LeBrun’s ALE Metrics with Negative Mass

In this article we investigate deformations of a scalar-flat Kähler metric on the total space of complex line bundles over ${\mathbb{CP}^1}$ constructed by C. LeBrun. In particular, we find that the metric is included in a one-dimensional family of such metrics on the four-manifold, where the complex structure in the deformation is not the standard one.     

Energy Momentum Distributions of Texture and?Monopole Metrics in General Relativity

The aim of this study is to investigate the energy-momentum distributions of texture and monopole topological defects metrics in general relativity (GR). For this aim Einstein, Bergmann-Thomson, Landau-Lifshitz (LL), M?ller and Papapetrou energy-momentum densities have been used in general relativity theory. We obtained that (i) for the texture metric only Einstein and Bergmann-Thomson energy densities give the same results but the others energy and momentum densities do not provide the same results in GR; (ii) for the monopole metric, while Einstein, Bergmann-Thomson and Papapetrou energy and momentum densities are giving the same energy-momentum results, M?ller and Landau-Lifshitz densities do not give the same energy results with the other definitions in GR.     

Affine Metrics: An Structure for Unification of?Gravitation and Electromagnetism

This paper is mainly intended to define a mathematical framework for unification of gravity and electromagnetism. The main idea is that affine concepts replace linear concepts in the context of general relativity. First, we introduce affine metrics on affine spaces,and then generalize semi-Riemannian manifolds to affine semi-Riemannian manifolds and investigate their associated connections and geodesics and curvatures. Then we apply these concepts to space-times in order to combine Maxwell’s and Einstein’s field equations into one equation.     

Nonholonomic Ricci Flows, Exact Solutions in Gravity, and?Symmetric and Nonsymmetric Metrics

We provide a proof that nonholonomically constrained Ricci flows of (pseudo) Riemannian metrics positively result into nonsymmetric metrics (as explicit examples, we consider flows of some physically valuable exact solutions in general relativity). There are constructed and analyzed three classes of solutions of Ricci flow evolution equations defining nonholonomic deformations of Taub NUT, Schwarzschild, solitonic and pp-wave symmetric metrics into nonsymmetric ones.     

Kähler Reduction of Metrics with Holonomy G<Subscript>2</Subscript>

A torsion-free G₂ structure admitting an infinitesimal isometry such that the quotient is a Kähler manifold is shown to give rise to a 4-manifold equipped with a complex symplectic structure and a 1-parameter family of functions and 2-forms linked by second order equations. Reversing the process in various special cases leads to the construction of explicit metrics with holonomy equal to G₂.     

Einstein Gravity in Almost Kähler Variables and Stability of Gravity with Nonholonomic Distributions and Nonsymmetric Metrics

We argue that the Einstein gravity theory can be reformulated in almost Kähler (nonsymmetric) variables with effective symplectic form and compatible linear connection uniquely defined by a (pseudo) Riemannian metric. A class of nonsymmetric theories of gravitation on manifolds enabled with nonholonomic distributions is considered. We prove that, for certain types of nonholonomic constraints, there are modelled effective Lagrangians which do not develop instabilities. It is also elaborated a linearization formalism for anholonomic noncommutative gravity theories models and analyzed the stability of stationary ellipsoidal solutions defining some nonholonomic and/or nonsymmetric deformations of the Schwarzschild metric. We show how to construct nonholonomic distributions which remove instabilities in nonsymmetric gravity theories. It is concluded that instabilities do not consist a general feature of theories of gravity with nonsymmetric metrics but a particular property of some models and/or unconstrained solutions.     

Integration in the GHP Formalism III: Finding Conformally Flat Radiation Metrics as an Example of an “Optimal Situation”

Held has proposed an integration procedure within the GHP formalism built around four real, functionally independent, zero-weighted scalars. He suggests that such a procedure would be particularly simple for the optimal situation, when the formalism directly supplies the full quota of four scalars of this type; a spacetime without any Killing vectors would be such a situation. Wils has recently obtained a conformally flat, pure radiation metric, which has been shown by Koutras to admit no Killing vectors, in general. In order to present a simple illustration of the ghp integration procedure, we obtain systematically the complete class of conformally flat, pure radiation metrics, which are not plane waves. Our result shows that the conformally flat, pure radiation metrics are a larger class than Wils has obtained.     

<Emphasis Type="Italic">D</Emphasis>-Dimensional Metrics with <Emphasis Type="Italic">D</Emphasis>−3 Symmetries

Symmetry transformations in a space of D-dimensional vacuum metrics with D?3 commuting Killing vectors are studied. We solve directly the Einstein equations in the Maison formulation under additional assumptions. We show that the Reissner-Nordström solution is related by the symmetry transformation to a particular case of the 5-dimensional Gross-Perry metric and the 5-dimensional plane wave solution is related to the Gross-Perry-Sorkin metric.