Relativistic corrections to the electromagnetic and axial moments of nuclei and other composite systems

Abstract

We calculate the electromagnetic and axial nuclear moments of the deuteron and triton as a function of their radius using a relativistic two-nucleon and three-nucleon model formulated on the light-cone. The results also provide an estimate of the nuclear binding corrections to helicity-dependent deep inelastic scattering sum rules. At large nucleon radius, the moments are given by the usual nonrelativistic formulae modified by finite binding effects. At small radius, the moments take the canonical values given by the generalization of the Drell-Hearn-Gerasimov sum rule. In addition, as R → 0, the constituent helicities become completely disoriented, and the Gamow-Teller matrix element vanishes. Thus, in the pointlike limit MR → 0, the moments of spin-one bound states coincide with the canonical couplings of elementary spin-one bosons of the Standard Model, μ = e M , Q = −e M 2 , and g a = 0. Similarly, in the case of spin-half systems, the magnetic moment approaches the Dirac value μ = e 2M , and the axial coupling g a vanishes.