Vertex Operators in $AdS_3\times S^3$ Background with NS_NS Flux using   Berkovits-Vafa-Witten Variables
  String equations for the vertex operators of type IIB on $AdS_3\times S^3$ background with NS-NS flux are calculated using Berkovits-Vafa-Witten formalism. With suitable field definitions, the linearized field equations for six-dimensional supergravity and a tensor multiplet on $AdS_3\times S^3$ are recovered from these. We also discuss the massless degrees of freedom that survive the $S^3$ Kaluza-Klein compactification and how our vertex operators are related to the vertex operators introduced by Giveon, Kutasov and Seiberg. 
M. Langham