Dr Andreas Jüttner, from the School of Physics and Astronomy at the University of Southampton, gave a seminar on computer simulation of Quantum Chromodynamics (QCD). QCD is the theory governing interactions between quarks and gluons within hadrons, such as protons and neutrons.
Dr Jüttner introduced the Standard Model of Particle Physics, a theory which very accurately predicts all phenomena we have been able to test experimentally. However, there are some puzzles which the Standard Model cannot explain. What is dark matter? Why is there more matter than anti-matter in the universe? And how can the Standard Model be reconciled with General Relativity? In order to find a theory beyond the Standard Model, we need to make increasingly accurate theoretical predictions to compare with experiment.
Unlike Electromagnetic and Weak interactions, QCD interactions cannot be treated analytically. Dr Jüttner explained the computational methods used to carry out QCD calculations numerically. Spacetime is discretised as a 4-dimensional lattice, with quark fields represented at lattice sites and gluon fields represented on the connections between lattice sites. Monte Carlo techniques are used to sample the possible configurations of the system, and these are used to compute the mean value of an observable.
This last step involves finding the inverse of a huge matrix (typically with (109)2 elements). This results in vast computations, requiring highly parallelised code. Because of this, Lattice QCD has driven a large amount of development in high performance computing, including IBM's Blue Gene series of supercomputers. It is important that Lattice QCD remains at the forefront of high performance computing, so that accurate predictions can be made to support results coming from particle experiments.