Dunbar, D., Bern, Z., & Dunbar, D. (1992). A mapping between Feynman and string motivated one-loop rules in gauge theories. Nuclear Physics B, 379(3), pp. 562-601. doi:10.1016/0550-3213(92)90135-X

Dunbar, David, Z. Bern, and D.C Dunbar. "A Mapping between Feynman and String Motivated One-loop Rules in Gauge Theories." Nuclear Physics B 379, no. 3 (1992): 562-601.

Dunbar, David, Z. Bern, and D.C Dunbar. "A Mapping between Feynman and String Motivated One-loop Rules in Gauge Theories." Nuclear Physics B 379.3 (1992): 562-601.