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In [[quantum field theory]], a '''tadpole''' is a one-loop [[Feynman diagram]] with one external leg, giving a contribution to a one-point [[correlation function (quantum field theory)|correlation function]] (i.e., the field's [[vacuum expectation value]]). One-loop diagrams with a [[propagator]] that connects back to its originating vertex are often also referred as tadpoles. For many theories, these graphs vanish in [[dimensional regularization]].
In [[quantum field theory]], a '''tadpole''' is a one-loop [[Feynman diagram]] with one external leg, giving a contribution to a one-point [[correlation function (quantum field theory)|correlation function]] (i.e., the field's [[vacuum expectation value]]). One-loop diagrams with a [[propagator]] that connects back to its originating vertex are often also referred as tadpoles. For many massless theories, these graphs vanish in [[dimensional regularization]].


[[Image:tadpole.png]]
[[Image:tadpole.png]]

Revision as of 11:21, 21 September 2007

In quantum field theory, a tadpole is a one-loop Feynman diagram with one external leg, giving a contribution to a one-point correlation function (i.e., the field's vacuum expectation value). One-loop diagrams with a propagator that connects back to its originating vertex are often also referred as tadpoles. For many massless theories, these graphs vanish in dimensional regularization.

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 spermion instead. 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).