Bonus Yangian Symmetry for the Planar S-Matrix of N=4 Super Yang-Mills
  Recent developments in the determination of the planar S-matrix of N=4 Super Yang-Mills are closely related to its Yangian symmetry. Here we provide evidence for a yet unobserved additional symmetry: the Yangian level-one helicity operator. 
Niklas Beisert, Burkhard U. W. Schwab
hep-th