By explicit calculations of four-field couplings, we observe that the higher derivative corrections to the DBI action in flat space-time, can be either in a covariant form or in a T-duality invariant form. The two forms ...

We calculate in details the sphere-level scattering amplitude of two Ramond-Ramond (RR) and two Neveu-Schwarz-Neveu-Schwarz (NSNS) vertex operators in type II superstring theories in Ramond-Neveu-Schwarz (RNS) formalism. ...

produces higher-derivative couplings of four strings. In this paper, we explicitly calculate the kinematic factor of four Ramond-Ramond (RR) states in the supergravity. Using this factor, we then find the eight-derivative P-even and P-odd couplings of four...