Dynamical Bar-Mode Instability in Differentially Rotating Magnetized Neutron Stars

This paper presents a numerical study over a wide parameter space of the likelihood of the dynamical bar-mode instability in differentially rotating magnetized neutron stars. The innovative aspect of this study is the incorporation of magnetic fields in such a context, which have thus far been neglected in the purely hydrodynamical simulations available in the literature. The investigation uses the Cosmos++ code which allows us to perform three dimensional simulations on a cylindrical grid at high resolution. A sample of Newtonian magneto-hydrodynamical simulations starting from a set of models previously analyzed by other authors without magnetic fields has been performed, providing estimates of the effects of magnetic fields on the dynamical bar-mode deformation of rotating neutron stars. Overall, our results suggest that the effect of magnetic fields are not likely to be very significant in realistic configurations. Only in the most extreme cases are the magnetic fields able to suppress growth of the bar mode.Comment: 12 pages, 16 figures. References added and minor edits made to match published versio

Three Dimensional Distorted Black Holes

We present three-dimensional, {\it non-axisymmetric} distorted black hole initial data which generalizes the axisymmetric, distorted, non-rotating [Bernstein93a] and rotating [Brandt94a] single black hole data developed by Bernstein, Brandt, and Seidel. These initial data should be useful for studying the dynamics of fully 3D, distorted black holes, such as those created by the spiraling coalescence of two black holes. We describe the mathematical construction of several families of such data sets, and show how to construct numerical solutions. We survey quantities associated with the numerically constructed solutions, such as ADM masses, apparent horizons, measurements of the horizon distortion, and the maximum possible radiation loss ($MRL$).Comment: 23 pages, 12 figures, accepted for publication in Classical and Quantum Gravit

Finding Apparent Horizons in Dynamic 3D Numerical Spacetimes

We have developed a general method for finding apparent horizons in 3D numerical relativity. Instead of solving for the partial differential equation describing the location of the apparent horizons, we expand the closed 2D surfaces in terms of symmetric trace--free tensors and solve for the expansion coefficients using a minimization procedure. Our method is applied to a number of different spacetimes, including numerically constructed spacetimes containing highly distorted axisymmetric black holes in spherical coordinates, and 3D rotating, and colliding black holes in Cartesian coordinates.Comment: 19 pages, 13 figures, LaTex, to appear in Phys. Rev. D. Minor changes mad

Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron

The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of $\sqrt s =1.96$ TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is $A_{\mathrm{FB}}^{t\bar{t}} = 0.128 \pm 0.025$. The combined inclusive and differential asymmetries are consistent with recent standard model predictions