Tadpole (physics)

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 is not stable in the vacuum.

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.