  By defining the heterotic Green-Schwarz superstring action on an N=(2,0)
super-worldsheet, rather than on an ordinary worldsheet, many problems with the
interacting Green-Schwarz superstring formalism can be solved. In the
light-cone approach, superconformally transforming the light-cone
super-worldsheet onto an N=(2,0) super-Riemann surface allows the elimination
of the non-trivial interaction-point operators that complicate the evaluation
of scattering amplitudes. In the Polyakov approach, the ten-dimensional
heterotic Green-Schwarz covariant action defined on an N=(2,0) super-worldsheet
can be gauge-fixed to a free-field action with non-anomalous N=(2,0)
superconformal invariance, and integrating the exponential of the covariant
action over all punctured N=(2,0) super-Riemann surfaces produces scattering
amplitudes that closely resemble amplitudes obtained using the unitary
light-cone approach.
