Singularity free cosmological solutions of Einstein-Maxwell equations

We report on a new two-parameter class of cosmological solutions to the Einstein-Maxwell equations. The solutions have everywhere regular curvature invariants. We prove that the solutions are geodesically complete and globally hyperbolic.Comment: 8 pages,latex; v2 some typos correcte

Killing spinor space-times and constant-eigenvalue Killing tensors

A class of Petrov type D Killing spinor space-times is presented, having the peculiar property that their conformal representants can only admit Killing tensors with constant eigenvalues.Comment: 11 pages, submitted to CQ

A new form of the Kerr solution

A new form of the Kerr solution is presented. The solution involves a time coordinate which represents the local proper time for free-falling observers on a set of simple trajectories. Many physical phenomena are particularly clear when related to this time coordinate. The chosen coordinates also ensure that the solution is well behaved at the horizon. The solution is well suited to the tetrad formalism and a convenient null tetrad is presented. The Dirac Hamiltonian in a Kerr background is also given and, for one choice of tetrad, it takes on a simple, Hermitian form.Comment: 8 pages, LaTeX, no figures. Corrected and improved version. To appear in Phys. Rev.

Gravitating superconducting strings with timelike or spacelike currents

We construct gravitating superconducting string solutions of the U(1)_{local} x U(1)_{global} model solving the coupled system of Einstein and matter field equations numerically. We study the properties of these solutions in dependence on the ratio between the symmetry breaking scale and the Planck mass. Using the macroscopic stability conditions formulated by Carter, we observe that the coupling to gravity allows for a new stable region that is not present in the flat space-time limit. We match the asymptotic metric to the Kasner metric and show that the relations between the Kasner coefficients and the energy per unit length and tension suggested previously are well fulfilled for symmetry breaking scale much smaller than the Planck mass. We also study the solutions to the geodesic equation in this space-time. While geodesics in the exterior space-time of standard cosmic strings are just straight lines, test particles experience a force in a general Kasner space-time and as such bound orbits are possible.Comment: 16 pages including 14 figure

Non-Leptonic Decays of B Mesons and Strong Coupling Constants

Non-leptonic decays of B mesons into two mesons or meson resonances are studied on the basis of two versions of simple pole-dominance models involving scalar, vector, pseudoscalar and axial-vector poles. The results are compared with those obtained from the usual factorization model and used to obtain information on strong coupling constants between B meson and one light or one charmed meson, respectively. These coupling constants are compared to results from various QCD sum rule calculations.Comment: Latex file 35 pages, including 3 figure

Is Context-aware Reasoning = Case-based Reasoning?

The purpose of this paper is to explore the similarities and differences and then argue for the potential synergies between two methodologies, namely Context-aware Reasoning and Case-based Reasoning, that are amongst the tools which can be used for intelligent environment (IE) system development. Through a case study supported by a review of the literature, we argue that context awareness and case based reasoning are not equal and are complementary methodologies to solve a domain specific problem, rather, the IE development paradigm must build a cooperation between these two approaches to overcome the individual drawbacks and to maximise the success of the IE systems

Electrovac pppp-waves

New exact solutions of the Einstein-Maxwell field equations that describe $pp$-waves are presented

Changes in Polarization Position Angle across the Eclipse in the Double Pulsar System

We investigate the changes in polarization position angle in radiation from pulsar A around the eclipse in the Double Pulsar system PSR J0737-3039A/B at the 20 cm and 50 cm wavelengths using the Parkes 64-m telescope. The changes are ~2\sigma\ during and shortly after the eclipse at 20 cm but less significant at 50 cm. We show that the changes in position angle during the eclipse can be modelled by differential synchrotron absorption in the eclipse regions. Position angle changes after the eclipse are interpreted as Faraday rotation in the magnetotail of pulsar B. Implied charge densities are consistent with the Goldreich-Julian density, suggesting that the particle energies in the magnetotail are mildly relativistic.Comment: Accepted for publication in The Astrophysical Journal Letter