High Energy Physics

Throughout history science has aimed at unification, whereby more phenomena are explained by more fundamental theories with simpler principles. We will discuss how string theory aims at being the ultimate unified theory of all elementary forces in nature.

Galaxy clusters are the biggest gravitationally bound structures in the Universe. Simple features of these objects can help us reconstruct the initial conditions at the Big-Bang and test the fundamental laws of physics.

The Large Hadron Collider was recently switched on, then broke and was switched on again. It has started producing collisions that probe Nature on the smallest distances yet reached. What broke when it was switched on? How does one detect what comes out of these collisions, and what can the result tell us about how Nature works on these scales? This talk briefly describes what we think we know, why it may be wrong, and whether (in either case) it will destroy the world.

Nonlinear numerical relativistic elasticity may be necessary for simulations including neutron star crusts. Basic simulations of large deformations in relativistic elastic matter will be detailed, and issues necessary for more realistic simulations covered. This work is in collaboration with Carsten Gundlach.

I present a relativistic study of axisymmetric magnetohydrodynamic Bondi--Hoyle accretion onto a moving Kerr black hole. The equations of general relativistic magnetohydrodynamics are solved using high resolution shock capturing methods, involving the use of linearised Riemann solvers. In this study I use the ideal MHD limit, which assumes no viscosity and infinite conductivity. The fluid flow is completely specified by the adiabatic constant $Gamma$, the asymptotic speed of sound $c_s^infty$, and the plasma beta parameter $beta_P$. In particular I restrict the investigation to asymptotically supersonic flows where $v_infty ge c_rms^infty$. To determine the stability of the flow I measure the accretion rates of the energy, and mass. The models presented in this study exhibit a matter density depletion in the downstream region of the black hole which tends to vacuum in convergence tests. This is a feature due to the presence of the magnetic field, more specifically the magnetic pressure, which is not seen in purely hydrodynamic studies. The models investigated present a tendency towards a steady state, which is in agreement with previous studies performed by Font and Iban'ez (1998) using a purely hydrodynamic model.

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.