On the $G_2$ Manifestation for Longitudinally Polarized
  The contribution of the $G_2$ structure function to polarized deep inelastic scattering is slightly redefined in order to avoid kinematical zeros. Its strong $Q^2$-dependence implied by the Burkhardt-Cottingham (BC) sum rule naturally explains the sign change of the generalized Gerasimov-Drell-Hearn (GDH) sum rule. The status of the BC sum rule and implications for other spin processes are discussed. 
Soffer and O.V.Teryaev