Feynman diagrams

Abstract It’s nevertheless an endless mess before one can assess Nature’s inventiveness. A Feynman diagram [l] is a graphical representation of the amplitude for a given process. It is composed of three types of elements: external lines, internal lines and vertices. With everyone of these elements one associates a mathematical expression, and the product of these expressions, in an appropriate order (together with some overall factors), yields the amplitude.The Feynman rules tell us which mathematical expression is to be associated with a given element of the Feynman diagram.