Tadpole (physics)

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In physics, a tadpole is a Feynman diagram with one external leg, which henceforth encodes a one-point function. The existence of a nonzero tadpole implies that the corresponding field has a nonzero VEV.

The physics of tadpoles and the word tadpole was invented by Sidney Coleman. The editor was not satisfied, but he changed his mind once Sidney Coleman proposed a new word - spermion. Both words are derived from the shape of the Feynman diagram: a circle with a line interval attached to its external side. Tadpole diagrams, in this sense, first appear in the above-mentioned article by Coleman and Glashow, Physical Review B v. 134, p.671 (1964). Although the term is often used in physics, it has not yet made it into the OED.