OPE's and the Dilaton Beta-Function for the 2-D N=1 Supersymmetric   Non-Linear $\sigma$-Model
  Using the superspace formalism, we compute for the two-dimensional N=1 supersymmetric non-linear $\sigma$-model, the order $(\alpha^{\prime})^{2}$ $(R_{mnpq})^2$ (three-loop) correction to the central charge via the operator product expansion of the supercurrent with itself. The contribution vanishes, in agreement with previous results obtained from the usual $\sigma$-model $\beta$-function approach. 
Marcia E. Wehlau