Abstract :
We analyse the interaction between the massless Ramond-Ramond states with a dilaton in a type II superstring. By constructing vertex operators for massless Ramond-Ramond states and computing their correlation functions with a dilaton we find the Ramond-Ramond part of the superstring low-energy effective action. Those RR terms appear in the action without the standard dilatonic factor (string coupling constant) as has been shown earlier on the basis of space-time supersymmetry. The geometrical interpretation of this fact is presented. Namely we argue that the spin operators in the RR vertices effectively decrease the Euler character of the worldsheet by 1 unit. As a result, the dilaton term in the worldsheet action has the form: ∼ ∫ d2z eΦΛFΛ where Λ and Λ are the (1, 0) and (0,1) spin operators for the ghost and matter fields, F is the RR field strength contracted with y-matrices. We also analyse the interaction of a dilaton with the massive RR states.
