Electromagnetic moments of quasi-stable baryons

Abstract

We address electromagnetic properties of quasi-stable baryons in the context of chiral extrapolations of lattice QCD results. For particles near their decay threshold we show that the application of a small external magnetic field changes the particle's energy in a non-analytic way. Conventional electromagnetic moments are only well-defined when the background field B satisfies |eB|/(2M_*|M_*-M-m|) where M_* is the mass of the resonance and M, m the masses of the decay products. An application of this situation is the chiral extrapolation of Delta(1232)-isobar electromagnetic properties. We discuss such an extrapolation of the Delta(1232)-isobar magnetic dipole, electric quadrupole and magnetic octupole moments by a covariant chiral effective field theory.