I am a postdoctoral researcher studying the nature of the strong nuclear force through numerical simulations of Quantum Chromodynamics (QCD) on supercomputers, in a field commonly referred to as Lattice QCD. I am a member of the nuclear and particle physics research group of the Jülich Supercomputing Centre at Forschungszentrum Jülich.

I completed my BSc (High Performance Computational Physics) (Honours) at The University of Adelaide in 2012, with an honours thesis focusing on visualisations of centre domains, structures that form in the quantum fluctuations of gluon fields in “empty space”. I stayed at the university to study for my PhD at the Special Research Centre for the Subatomic Structure of Matter, working with Prof. Derek Leinweber to investigate the structure of protons and neutrons, and their excited states.


Visualisations of QCD

When we consider the world on a quantum scale, we find that “empty space” is not actually empty. It is full of quantum fluctuations corresponding to all of the particles in the standard model. In particular gluons, which carry the strong nuclear force, are able to interact with each other, allowing their quantum fluctuations to form complicated structures. One such structure is the centre domain.

By considering a quantity known as the local Polyakov loop, we find regions of space in which all of the Polyakov loops take similar values, clustering near one of three complex phases. These regions are called centre domains. By colouring the centre domains associated with each phase red, green, and blue, we can visualise all of the centre domains within a small cube of empty space as seen in this video.

It turns out that these centre domains are deeply connected to the phenomenon of confinement, that binds quarks together to form hadrons such as protons and neutrons. The size of these domains governs the size of the core of protons, neutrons and other hadrons.

Structure of protons and neutrons

Protons and neutrons are made up of smaller particles known as quarks. Because of this, they have an internal structure that we can investigate by probing them with electromagnetic fields.

Experiments do this by firing electrons at proton or neutron targets and measuring the way they scatter. This allows the electric and magnetic form factors to be measured. These are functions of the momentum transferred between the electron and the target that are related to the distributions of charge and magnetism inside the target respectively.

Using lattice QCD, we can compute theoretical predictions of these form factors from first principles. Existing techniques can do this well when the target is at rest, but in order to study a range of momentum transfers, the target must be moving. Under these conditions, the particles we create on the lattice start to mix with similar particles of different parities, spoiling the result.

We have developed the parity-expanded variational analysis (PEVA) technique to deal with this problem, and allow a clean extraction of the form factors of interest. For example, these plots show extractions of the electric and magnetic form factors of the proton and neutron.