Strangeness and Charge Symmetry Violation in Nucleon Structure

This thesis discusses two key topics: strangeness and charge symmetry violation (CSV) in the nucleon. It also provides a pedagogical introduction to chiral effective field theory tailored to the high-precision era of lattice quantum chromodynamics (QCD). Because the nucleon has zero net strangeness, strange observables give tremendous insight into the nature of the vacuum; they can only arise through quantum fluctuations in which strange-antistrange quark pairs are generated. As a result, the precise values of these quantities within QCD are important in physics arenas as diverse as precision tests of QCD, searches for physics beyond the Standard Model, and the interpretation of dark matter direct-detection experiments. Similarly, the precise knowledge of CSV observables has, with increasing experimental precision, become essential to the interpretation of many searches for physics beyond the Standard Model. In this thesis, the numerical lattice gauge theory approach to QCD is combinedwith the chiral perturbation theory formalism to determine strange and CSV quantities in a diverse range of observables including the octet baryon masses, sigma terms, electromagnetic form factors, and parton distribution functions. This thesis builds a comprehensive and coherent picture of the current status of understanding of strangeness and charge symmetry violation in the nucleon.

Auteur
Dr. Phiala Shanahan graduated from the University of Adelaide in Australia in 2011 with a Bachelor of Science in High Performance Computational Physics with 1st class honors, the University Medal, and the Australian Institute of Physics Bragg Medal. Dr. Shanahan's doctoral work, completed under the supervision of Professor Anthony Thomas and Dr. Ross Young, won the Centre for the Subatomic Structure of Matter doctoral prize, as well as the university prize for the best thesis in the faculty of sciences. In 2015, Dr. Shanahan began a postdoctoral appointment at the Massachusetts Institute of Technology in the United States.

Contenu
Introduction.- Quantum Chromodynamics.- Chiral Perturbation Theory.- Octet Baryon Mass Splittings.- Sigma Commutators.- Parton Distribution Moments.- Electromagnetic Form Factors.- Summary and Outlook.