Chiral magnetism of the nucleonT.R. Hemmert1, 2 and W. Weise1, 3
1 Physik Department, Theoretische Physik, Technische Universität München, D-85747 Garching, Germany
2 Nuclear Theory Group (Visiting Scholar.) , Department of Physics, University of Washington, Seattle, WA 98195, USA
3 ECT*, Villa Tambosi, I-38050 Villazzano (Trento), Italy
(Received: 23 April 2002 / Revised version: 17 July 2002 / Published online: 17 December 2002)
We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons, pions and delta-resonances as explicit degrees of freedom. We point out that the usual power counting applied so far to this problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified power counting and compare the resulting chiral extrapolation function to available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here are consistent with the Padé fit ansatz introduced by the Adelaide group a few years ago.
11.10.-z - Field theory.
12.38.Gc - Lattice QCD calculations.
11.30.Rd - Chiral symmetries.
© Società Italiana di Fisica, Springer-Verlag 2002