The sum rules for the spin dependent structure functions $g_1$ in the   isovector reaction
  In the isovector reaction, the sum rule for the spin dependent function $g_1$ which is related to the cross section of the photoproduction is derived. In the small $Q^2$ region, the sum rule is dominated by the low energy contribution and it tightly connects the resonance, the elastic, and the non-resonant contributions. 
Susumu Koretune