Boundary term, extended Witten identities and positivity of energy
  In terms of two-spinors a chiral formulation of general relativity with the Ashtekar Lagrangian and its Hamiltonian formalism in which the basic dynamic variables are the dyad spinors are presented. The extended Witten identities are derived. A new expression of the Hamiltonian boundary term is obtained. Using this expression and the extended Witten identities the proof of the positive energy theorem is extended to a case including momentum and angular momentum. 
G. Y. Chee, Jingfei Zhang and Yongxin Guo