LORENTZ-COVARIANT GREEN-SCHWARZ SUPERSTRING AMPLITUDES

In a recent paper, the BRST formalism for the gauge-fixed N = 2 twistor-string was used to calculate Green-Schwarz superstring scattering amplitudes with an arbitrary number of loops and external massless states. Although the gauge-fixing procedure preserved the worldsheet N = 2 superconformal invariance of the twistor-string, it broke the target-space SO(9,1) super-Poincare invariance down to an SU(4) x U(1) subgroup. In this paper, generators for the SO(9,1) super-Poincare transformations, as well as manifestly covariant vertex operators, are explicitly constructed out of the gauge-fixed matter fields. The earlier calculated amplitudes are then expressed in manifestly Lorentz-covariant notation.