High Energy Physics

Alfven oscillations of strongly magnetized neutron stars coupled to shear modes in the solid crust could possibly explain the quasi-periodic oscillations (QPOs) observed in the giant flares of soft gamma repeaters. We present results of two-dimensional simulations of Alfven torsional oscillations in magnetars, modeled as relativistic stars with a dipolar magnetic field. We use a general relativistic magnetohydrodynamics code in the anelastic approximation, which allows for an effective suppression of fluid modes and an accurate description of the Alfven waves. We discuss the coupling of the neutron star interior with the magnetosphere and the observational consequences.

I will discuss the techniques that can be used to include arbitrary equations of state in MHD simulations, particularly the ways in which one may perform conservative to primitive variable conversion numerically for such simulations.

GPUs can offer a less costly solution to large-scale calculations of astrophysical systems. I will outline the basics of the CUDA libraries and also compare with various metrics our in-development GPU code for molecular dynamics versus our hybrid OpenMP/MPI version.

Neutron star mergers represent one of the most promising sources of gravitational waves (GW), while that the presence of strong magnetic fields may offer the possibility of a characteristic electromagnetic signature allowing for concurrent detection. In this talk will be presented a new hybrid-passive approach to match the full GR-MHD evolutions of the binary neutron star mergers to the force-free equations in order to study numerically the dynamics and interaction of their magnetospheres.

Black hole-neutron star (BHNS) binary mergers areimportant gravitational wave sources and (possibly) gamma ray burst progenitors. Fully relativisticsimulations have only recently begun to try to capture neutron star physics beyond the polytrope approximation. In this talk we discuss the numerical challenges of replacing polytropes with realistic neutron stars--particularly those relating to sharper neutron star surface features and to the effects of neutrino radiation--and we present the current status of simulations by the (Caltech-Cornell-CITA-WSU) SXS collaboration and how they are dealing with these issues.

The Einstein Toolkit Consortium is developing and supporting open software for relativistic astrophysics. Our aim is to provide the core computational tools that can enable new science, broaden the community, facilitate interdisciplinary research, and take advantage of emerging petascale computers and advanced cyberinfrastructure. The Einstein Toolkit currently consists of an open set of over 100 components for computational relativity along with associated tools for simulation management and visualization. The toolkit includes a vacuum spacetime solver, a relativistic hydrodynamics solver, along with components for initial data, analysis, and computational infrastructure. These components have been developed and improved over many years by many different contributors.

New equations of state (EOSs) from extensive virial and relativistic mean field calculations will be presented. We construct thermodynamically consistent EOSs from slightly noisy free energy calculations, which satisfy the first law, and conserves entropy during adiabatic compression. However this requires a very careful procedure of numerically smoothing the entropy and then integrating the entropy to generate consistent free energies. We discuss various features of the EOS in different density, temperature, and proton fraction regimes. We compare the adiabatic index for our EOSs with those of the Lattimer Swesty and H. Shen et al. EOSs. We do not find a first order liquid vapor phase transition for the astrophysical EOS. Finally, we discuss neutrino interactions that are consistent with our EOSs. At low density, we present model independent neutrino responses that are based on the viral expansion .