


Question
What are Feynman diagrams? Could you give good bibliography about QED?
Asked by: Miguel Angel de Blas
Answer
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 timedependent
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 nontechnical 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 midlevel 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

