Form factor (Quantum Field Theory)
- Form factor (Quantum Field Theory)
In effective field theory, a "form factor" is a function which gives the properties of a certain particle interaction without including all of the underlying physics. It is measured experimentally when a theoretical calculation is unavailable or too difficult.
For example, at low energies the interaction of a photon with a nucleon is a very complicated calculation involving interactions between the photon and a sea of quarks and gluons, and often the calculation cannot be done.
However the general form of the interaction is known,
where represents the photon momentum. The three functions, , can be measured experimentally, and then the three effective vertices can be used to perform calculations that would otherwise be too difficult.
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