Effective field theory for nucleons and light nuclei

We plan to study the properties of single nucleons and light nuclei using field theories of nucleons, pions and photons. The 'effective' theories respect the symmetries of the underlying theory of the strong interaction: quantum chromodynamics (QCD). We plan to improve the description of nucleon properties in these theories, and to use them to determine the forces between nucleons in a model-independent way. The results will be applied to the calculations of the interactions of photons with few-nucleon systems. Of particular interest is Compton scattering which provides a very sensitive probe of the internal structure of the nucleon since it can be used to determine the complete set of polarisabilities which describe the repsonse fo a nucleon to an electromagnetic field. In the case of the neutron, our work will help with extracting these polarisabilities from experiments on light nuclei. These theories allow us to write nucleon properties as power series in the mass of the pion, which is a measure of how strongly the chiral symmetry of QCD is broken by the quark masses. Current simulations of QCD on large space-time lattices are carried out using quark masses that are much larger than those in the real world. Our expansions of nucleon properties will be needed to extrapolate the results of these calculations to realistic quark masses.