String amplitudes in the Hpp-wave limit of AdS3xS3
  We compute string amplitudes on pp-waves supported by NS-NS 3-form fluxes and arising in the Penrose limit of AdS3xS3xM. We clarify the role of the non-chiral accidental SU(2) symmetry of the background. We comment on the extension of our results to the superstring and propose a holographic formula in the BMN limit of the AdS3/CFT2 correspondence valid for any correlator. 
M. Bianchi, G. D'Appollonio, E. Kiritsis, O. Zapata