Three-Graviton Amplitude in Berkovits-Vafa-Witten Variables
  We compute the three-graviton tree amplitude in Type IIB superstring theory compactified to six dimensions using the manifestly (6d) supersymmetric Berkovits-Vafa-Witten worldsheet variables. We consider two cases of background geometry: the flat space example R6xK3, and the curved example AdS3xS3xK3 with Ramond flux, and compute the correlation functions in the bulk. 
K. Bobkov and L. Dolan