QUESTION #263

# What are Feynman diagrams? Could you give good bibliography about QED?

Asked by: Miguel Angel de Blas

Feynman diagrams are a visual summary of a quantum mechanical calculation. When quantum field theory was still in its infancy in the 1930s and 1940s the principal technique for computing the probability for a certain particle interaction to occur was time-dependent perturbation theory in relativistic quantum mechanics. The basics of this calculational technique can be found in any advanced quantum mechanics textbook. Feynman, Schwinger and Tomonaga (and many others) improved this old technique and developed the modern version of quantum field theory we use today (they won the Nobel prize for this, see http://www.slac.stanford.edu/library/nobel.html).

Feynman realized that the somewhat lengthy sums of integrals can be conveniently summarized as a sum of diagrams. The diagram acts like a recipe: take these incoming particles, have them annihilate into some intermediate particle, and then have this intermediate particle decay into some final state particles. Integrate over the intermediate particle's momentum and impose energy/momentum conservation. The graphical shorthand is very convenient and appeals to our intuitive sense that physics is local -- interactions occur when particles are at the same spacetime point (the vertices in a Feynman diagram), like billiard balls bouncing off one another. A nice graphical description of these things is provided at: http://www2.slac.stanford.edu/vvc/theory/feynman.html.

As for a bibliography, QED can be found in all quantum field theory textbooks. You can read some non-technical books such as Feynman's own 'QED: The Strange Theory of Light and Matter,' or 'QED and the Men Who Made It' by S. Schweber.

Very introductory descriptions of particle physics, quantum field theory and general Feynman diagrams can be found in: Introduction to High Energy Physics, D. Perkins Introduction to Elementary Particles, D. Griffiths

A mid-level treatment is given in Quarks and Leptons: An Introductory Course in Modern Particle Physics, by F. Halzen and A. Martin.

The standard references for graduate students are Relativistic Quantum Fields, by Bjorken and Drell Introduction to Quantum Field Theory, by M. Peskin and V. Schroeder

Answered by: Brent Nelson, M.A. Physics, Ph.D. Student, UC Berkeley