Postgraduate Opportunities

Aspects of Nucleon Structure and Chiral Perturbation Theory

Although QCD is firmly established as the correct theory which describes the behaviour of quarks and gluon, and has been well tested at high energies, it is much harder to apply it to ordinary matter such as protons and neutrons at low energies. The reason is that, unlike the Coulomb force, the interactions between coloured objects gets stronger at larger distances, so that they never exist on their own but always in combinations (called hadrons). Barring intensive computer simulations (which have their own problems of interpretation), the most promising approach to understanding the structure and interactions of matter involves so-called ‘effective field theories’ which respect the symmetries of QCD but are formulated in terms of observable particles – protons, photons, pions etc. and this is called ‘Chiral perturbation theory’. Such theories have taught us, for instance, that the degree to which protons and neutrons are electrically polarised by a background field is almost exclusively due to the pion cloud which surrounds them.

Projects in this field could take a number of forms, depending on the student's interest. Although the field is more than fifteen years old there are some unresolved theoretical issues, concerned for instance with the agreement (or lack of it) between relativistic and non-relativistic formulations, and with whether and how to include heavier hadrons such as excited protons (Deltas). There are also more practical projects which involve using the established theory to calculate cross sections for observable processes, then comparing the results with the modern, high-precision data which is being generated at an number of labs round the world. For many years the properties of the constituents of ‘ordinary’ matter were neglected as experimentalists sought to reach higher and higher energies; happily these days this situation is being rectified. Extensions to simple nuclei are also of current interest, partly because only that way can we probe the properties of the neutron.

Research Groups

• Theoretical Physics

Judith McGovern is  a senior lecturer and former  Director of Teaching in the School of Physics and Astronomy.  She is originally from Edinburgh, and completed an undergraduate degree in Natural Sciences at the University of Cambridge before moving to Manchester to do a PhD in theoretical Nuclear Physics.  After a period as a postdoctoral associate at the University of Tübingen, she returned to Manchester as a lecturer. 

• Interface between Nuclear and Particle Physics
• Nucleon structure
• Compton Scattering from nucleons and light nuclei
• Effective Field Theories for nuclerar physics, especially Chiral Perturbation Theory