IIA string instanton corrections to the four-fermion correlator in the   intersection of Del Pezzo surfaces
  The Becker-Becker-Strominger formula, describing the string world-sheet instanton corrections to the four-fermion correlator in the Calabi-Yau compactified type-IIA superstrings, is calculated in the special case of the Calabi-Yau threefold realized in the intersection of two Del Pezzo surfaces. We also derive the selection rules in the supersymmetric GUT of the Pati-Salam type associated with our construction. 
Andrei Cheshel (Kaiserslautern U.) and Sergei V. Ketov (Tokyo   Metropolitan U.)