Natalia Saulina et al explore contributions to the 4D effective superpotential which arise from Euclidean D3 branes

Bogdan Florea, Shamit Kachru, John McGreevy, and Natalia Saulina (2007) Stringy instantons and quiver gauge theories. Journal of High Energy Physics, 5, Art. No. 024, May 2007. CaltechAUTHORS