Nonlocal Charges for Bonus Yangian Symmetries of Super-Yang-Mills
  The existence of a "bonus" U(1) level-one Yangian symmetry of N=4 super-Yang-Mills has recently been proposed. We provide evidence for this proposal by constructing the BRST-invariant nonlocal charge in the pure spinor sigma model corresponding to this bonus level-one symmetry. We also construct analogous charges for bonus U(1) symmetries at all odd levels of the Yangian. 
Nathan Berkovits and Andrei Mikhailov (IFT-UNESP, Sao Paulo)
hep-th