Regular Article - Theoretical Physics
Sum rule for the Compton amplitude and implications for the proton–neutron mass difference
Albert Einstein Center for Fundamental Physics, Institut für theoretische Physik, Universität Bern, Sidlerstrasse 5, 3012, Bern, Switzerland
2 Helmholtz-Institut für Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universität Bonn, Nussallee 14-16, 53115, Bonn, Germany
Accepted: 29 October 2020
Published online: 5 December 2020
The Cottingham formula expresses the leading contribution of the electromagnetic interaction to the proton-neutron mass difference as an integral over the forward Compton amplitude. Since quarks and gluons reggeize, the dispersive representation of this amplitude requires a subtraction. We assume that the asymptotic behaviour is dominated by Reggeon exchange. This leads to a sum rule that expresses the subtraction function in terms of measurable quantities. The evaluation of this sum rule leads to .
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