1. Rotating solutions in critical Lovelock gravitiesMirjam Cvetič, XingHui Feng, Hong Lü, Christopher N. Pope, 2017, izvirni znanstveni članek Opis: For appropriate choices of the coupling constants, the equations of motion of Lovelock gravities up to order n in the Riemann tensor can be factorized such that the theories admit a single (A)dS vacuum. In this paper we construct two classes of exact rotating metrics in such critical Lovelock gravities of order n in d = 2n +1 dimensions. In one class, the n angular momenta in the n orthogonal spatial 2planes are equal, and hence the metric is of cohomogeneity one. We construct these metrics in a KerrSchild form, but they can then be recast in terms of BoyerLindquist coordinates. The other class involves metrics with only a single nonvanishing angular momentum. Again we construct them in a KerrSchild form, but in this case it does not seem to be possible to recast them in BoyerLindquist form. Both classes of solutions have naked curvature singularities, arising because of the over rotation of the configurations. Ključne besede: astrophysics, nuclear physics Objavljeno: 08.03.2018; Ogledov: 925; Prenosov: 305 Celotno besedilo (274,39 KB) Gradivo ima več datotek! Več...

2. Electrodynamics of black holes in STU supergravityMirjam Cvetič, G. W. Gibbons, Christopher N. Pope, Zain H. Saleem, 2014, izvirni znanstveni članek Opis: External magnetic fields can probe the composite structure of black holes in string theory. With this motivation we study magnetised fourcharge black holes in the STU model, a consistent truncation of maximally supersymmetric supergravity with four types of electromagnetic fields. We employ solution generating techniques to obtain Melvin backgrounds, and black holes in these backgrounds. For an initially electrically charged static black hole immersed in magnetic fields, we calculate the resultant angular momenta and analyse their global structure. Examples are given for which the ergoregion does not extend to infinity. We calculate magnetic moments and gyromagnetic ratios via Larmor's formula. Our results are consistent with earlier special cases. A scaling limit and associated subtracted geometry in a single surviving magnetic field is shown to lift to AdS(3) x S2. Magnetizing magnetically charged black holes give static solutions with conical singularities representing strings or struts holding the black holes against magnetic forces. In some cases it is possible to balance these magnetic forces. Ključne besede: black holes, supergravity, string theory, conformal field models, string duality Objavljeno: 27.06.2017; Ogledov: 556; Prenosov: 311 Celotno besedilo (563,26 KB) Gradivo ima več datotek! Več...

3. Compactifications of deformed conifolds, branes and the geometry of qubitsMirjam Cvetič, G. W. Gibbons, Christopher N. Pope, 2016, izvirni znanstveni članek Opis: We present three families of exact, cohomogeneityone Einstein metrics in (2n + 2) dimensions, which are generalizations of the Stenzel construction of Ricciflat metrics to those with a positive cosmological constant. The first family of solutions are FubiniStudy metrics on the complex projective spaces CPn+1, written in a Stenzel form, whose principal orbits are the Stiefel manifolds V2(Rn+2) = SO(n+2)/SO(n) divided by Z(2). The second family are also EinsteinKahler metrics, now on the Grassmannian manifolds G(2)(Rn+3) = SO(n+3)/((SO(n+1)xSO(2)), whose principal orbits are the Stiefel manifolds V2(Rn+2) (with no Z(2) factoring in this case). The third family are Einstein metrics on the product manifolds Sn+1 x Sn+1, and are Kahler only for n = 1. Some of these metrics are believed to play a role in studies of consistent string theory compactifications and in the context of the AdS/CFT correspondence. We also elaborate on the geometric approach to quantum mechanics based on the Kahler geometry of FubiniStudy metrics on CPn+1, and we apply the formalism to study the quantum entanglement of qubits. Ključne besede: conformal field models, string theory, models of quantum gravity, differential geometry, algebraic geometry Objavljeno: 27.06.2017; Ogledov: 516; Prenosov: 303 Celotno besedilo (586,14 KB) Gradivo ima več datotek! Več...

4. SupergeometrodynamicsMirjam Cvetič, G. W. Gibbons, Christopher N. Pope, 2015, izvirni znanstveni članek Opis: We present explicit solutions of the timesymmetric initial value constraints, expressed in terms of freely specifiable harmonic functions for examples of supergravity theories, which emerge as effective theories of compactified string theory. These results are a prerequisite for the study of the timeevolution of topologically nontrivial initial data for supergravity theories, thus generalising the "Geometrodynamics" program of EinsteinMaxwell theory to that of supergravity theories. Specifically, we focus on examples of multiple electric Maxwell and scalar fields, and analyse the initial data problem for the general EinsteinMaxwellDilaton theory both with one and two Maxwell fields, and the STU model. The solutions are given in terms of up to eight arbitrary harmonic functions in the STU model. As a byproduct, in order compare our results with known static solutions, the metric in isotropic coordinates and all the sources of the nonextremal black holes are expressed entirely in terms of harmonic functions. We also comment on generalizations to timenonsymmetric initial data and their relation to cosmological solutions of gauged socalled fake supergravities with positive cosmological constant. Ključne besede: black holes, supergravity, string theory, conformal field models, string duality Objavljeno: 14.06.2017; Ogledov: 604; Prenosov: 91 Celotno besedilo (581,40 KB) Gradivo ima več datotek! Več...
