Spinor Decomposition of SU(2) Gauge Potential and The Spinor Structures   of Chern-Simons and Chern Density
  In this paper, the decomposition of SU(2) gauge potential in terms of Pauli spinors is studied. Using this decomposition, the spinor strutures of the Chern-Simons form and the Chern density are obtained. Furthermore, by these spinor structures, the knot quantum number of non-Abelian gauge theory is discussed, and the second Chern number is characterized by the Hopf indices and the Brouwer degrees of $\phi $-mapping. 
Yi-shi Duan, Xin Liu and Li-bin Fu