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Quantum electrodynamics (QED) is a quantum field theory of electromagnetism. QED describes all phenomena involving electrically charged particles interacting by means of the electromagnetic force and has been called "the
jewel of physics" for its extremely accurate predictions of quantities like the anomalous magnetic moment of the muon, and the Lamb shift of the energy levels of hydrogen.
Mathematically, QED has the structure of an Abelian gauge theory with a U(1) gauge group. The gauge field which mediates the interaction
between the charged spin-1/2 fields is the electromagnetic
field. Physically, this translates to the picture of charged particles interacting with each other by the exchange of
photons.
QED was the first quantum field theory in which the difficulties of building a consistent, fully quantum description of fields
and creation and annihilation of quantum particles were satisfactorily resolved. Sin-Itiro Tomonaga, Julian Schwinger and
Richard Feynman received the 1965 Nobel Prize in Physics for its
development, their contributions involving a covariant and gauge invariant prescription for the calculation of observable quantities.
The renormalization procedure for making sense of some of the
infinite predictions of quantum field theory also found its
first successful implementation in quantum electrodynamics.
The QED Lagrangian for the interaction of electrons and positrons through photons is
-
and its Dirac adjoint are the
fields representing electrically charged particles, specifically electron and positron fields represented as Dirac spinors.
is the gauge covariant derivative, with the coupling
strength (equal to the elementary charge), the covariant
vector potential of the electromagnetic field and the electromagnetic field tensor.
The part of the Lagrangian containing the electromagnetic
field tensor describes the free evolution of the electromagnetic field, whereas the Dirac-like
equation with the gauge covariant
derivative describes the free evolution of the electron and positron fields as well as their interaction with the
electromagnetic field.
See also Quantum field theory, Gauge theory, Renormalization, Standard Model.
References
- R. P. Feynman, QED: The strange theory of light and matter [ISBN 0691024170]
- Claude Cohen-Tannoudji, Jacques Dupont-Roc, Gilbert Grynberg, Photons and Atoms : Introduction to Quantum
Electrodynamics (John Wiley & Sons, 1997) [ISBN 0471184330]
- J. M. Jauch, F. Rohrlich, The Theory of Photons and Electrons (Springer-Verlag, 1980)
- R. P. Feynman, Quantum Electrodynamics (Perseus Publishing, 1998) [ISBN 0201360756]
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