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. 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 . Tadpole corrections are needed if the corresponding external field has a non-zero vacuum expectation value, such as the Higgs field.