Aspects of Nucleon Structure in Chiral Perturbation Theory

Abstract

The size of the proton is not yet fully understood, with a significant discrepancy between results obtained from Lamb shift measurements on electronic and muonic hydrogen. An independent value for the proton radius may be obtained from measurements on deuterium, but for an accurate calculation a detailed understanding of the deuteron’s structure is needed. In this thesis we present a calculation of structure contributions to the Lamb shift in muonic deuterium, using heavy-baryon chiral perturbation theory (HBChPT ), a low energy effective theory of QCD that describes the interactions of mesons and baryons. We show how the leading structure contributions to the Lamb shift come from a two-photon exchange diagram, and demonstrate the frameworks that are used in theoretical calculations of the Lamb shift. We then outline a calculation of the Compton tensor, using a hybrid approach in which intermediate rescattering states are treated in ordinary quantum mechanics. The results of this calculation are used to compute the inelastic Lamb shift, and our results are compared with those from other calculations. Finally we present our concluding remarks, summarising our work and suggesting how it may be carried forward.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jonathan Billowes (Supervisor) & Judith McGovern (Supervisor)