17 Facts About Feynman diagram

Feynman diagram used Ernst Stueckelberg's interpretation of the positron as if it were an electron moving backward in time.

Feynman diagram is a graphical representation of a perturbative contribution to the transition amplitude or correlation function of a quantum mechanical or statistical field theory.

Each Feynman diagram is the sum of exponentially many old-fashioned terms, because each internal line can separately represent either a particle or an antiparticle.

Feynman diagram is a representation of quantum field theory processes in terms of particle interactions.

Traditionally, the bottom of the Feynman diagram is the past and the top the future; other times, the past is to the left and the future to the right.

The law of summation is in accord with the principle of superposition—every Feynman diagram contributes to the total amplitude for the process.

Feynman diagram represents a perturbative contribution to the amplitude of a quantum transition from some initial quantum state to some final quantum state.

Feynman diagram is a graphical representation of a single summand in the Wick's expansion of the time-ordered product in the th-order term of the Dyson series of the -matrix,.

Forest Feynman diagram is one where all the internal lines have momentum that is completely determined by the external lines and the condition that the incoming and outgoing momentum are equal at each vertex.

An example of a tree Feynman diagram is the one where each of four external lines end on an.

Diagram that is not a forest Feynman diagram is called a loop Feynman diagram, and an example is one where two lines of an are joined to external lines, while the remaining two lines are joined to each other.

Example, consider the Feynman diagram formed from two external lines joined to one, and the remaining two half-lines in the joined to each other.

Symmetry factor theorem gives the symmetry factor for a general diagram: the contribution of each Feynman diagram must be divided by the order of its group of automorphisms, the number of symmetries that it has.

An automorphism of a Feynman diagram graph is a permutation of the lines and a permutation of the vertices with the following properties:.

Roughly speaking, a Feynman diagram is called connected if all vertices and propagator lines are linked by a sequence of vertices and propagators of the diagram itself.

Rules for spin- Dirac particles are as follows: The propagator is the inverse of the Dirac operator, the lines have arrows just as for a complex scalar field, and the Feynman diagram acquires an overall factor of -1 for each closed Fermi loop.

Feynman diagram discovered it after a long process of trial and error, since he lacked a proper theory of Grassmann integration.