Eur. Phys. J. A (2006) 28: 71-80
https://doi.org/10.1140/epja/i2006-09-008-3

MAMI 2005

Two-photon physics

¹ Physics Department, The College of William & Mary, 12000 Jefferson Ave, 23187, Williamsburg, USA
² Theory Group, Jefferson Lab, 23606, VA, USA
³ 12000 Jefferson Ave, 23606, Newport News, USA
⁴ 12000 Jefferson Ave, 23606, VA, USA

^* e-mail: marcvdh@jlab.org

Received: 12 May 2006
Accepted: 12 May 2006
Published online: 15 May 2006

Abstract

It is reviewed how Compton scattering sum rules relate low-energy nucleon structure quantities to the nucleon excitation spectrum. In particular, the GDH sum rule and recently proposed extensions of it will be discussed. These extensions are sometimes more calculationally robust, which may be an advantage when estimating the chiral extrapolations of lattice QCD results, such as for anomalous magnetic moments. Subsequently, new developments in our description of the nucleon excitation spectrum will be discussed, in particular a recently developed chiral effective field theory framework for the Δ(1232)-resonance region. Within this framework, we discuss results on N and Δ masses, the γNΔ transition and the Δ magnetic dipole moment.