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Vertex function
open-in-new
<p>In <a href="/facts/Quantum_electrodynamics/zPteAr6G">quantum electrodynamics</a>, the vertex function describes the coupling between a <a href="/facts/Photon/mFNhAEzA">photon</a> and an <a href="/facts/Electron/L0KBo5cW">electron</a> beyond the leading order of <a href="/facts/Perturbation_theory_(quantum_mechanics)/lYGgk9Ph">perturbation theory</a>. In particular, it is the <a href="/facts/One_particle_irreducible_correlation_function/slyeRgDh">one particle irreducible correlation function</a> involving the <a href="/facts/Fermion/LEckdDsR">fermion</a> ψ {\displaystyle \psi } , the antifermion ψ ¯ {\displaystyle {\bar {\psi }}} , and the <a href="/facts/Vector_potential/GgvfE8AM">vector potential</a> A. </p>