Experimental study of isovector spin sum rules
  We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for $0.05<Q^{2}<2.92$ GeV$^2$. The integral is fit to extract the twist-4 element $f_{2}^{p-n}$ which appears to be relatively large and negative. Systematic studies of this higher twist analysis establish its legitimacy at $Q^{2}$ around 1 GeV$^{2}$. We also performed an isospin decomposition of the generalized forward spin polarizability $\gamma_{0}$. Although its isovector part provides a reliable test of the calculation techniques of Chiral Perturbation Theory, our data disagree with the calculations. 
A. Deur, P. Bosted, V. Burkert, D. Crabb, V. Dharmawardane, G. E.   Dodge, T. A. Forest, K. A. Griffioen, S. E. Kuhn, R. Min...