Feynman diagram Outline Motivation Feynman integral Pertubation Thoery

Feynman diagram

Outline • • Motivation Feynman integral Pertubation Thoery in Quantum Mechanics Pertubation Thoery in Quantum Field Theory Green Function Feynman Diagram Experimental Connection

Motivation • Compared with experiments – Amplitude of final states from collision of two initial particles – Cross section of collision – Graphical representation and simplicity

Pertubation Thoery in Quantum Mechanics • Idea of Pertubation theory H = H_0 + H_I • Acquire information from H_0 Getting new eigenvector

Pertubation Thoery in Quantum Mechanics • Dyson series • How wave function evolute by time when H = H_0 + H_I

Pertubation Thoery in Quantum Field Theory • Idea of Quantum Field Theory – Number of particle – Take particle and wave as the same – Solution (Feynman path integral approach)

Pertubation Thoery in Quantum Field Theory • <final| exp( int_ (dt H_I)) |initial>

Green function • Ideal of Green function • Two point Green function • Four point Green function as combination of two point green function

Green function • Ideal of Green function • Four point Green function as combination of two point green function

Feynman Diagram • Green function + time evolution of field • Graphical representation

Feynman Diagram • Feynman rule: example of lampta Phy^4 theory

Feynman Diagram • Re-intepretation of anti-particle – Anti-particle in Dirac equation – Anti-charge and positive energe

Experimental Connection • Cross section – What’s cross section? – Connection of cross section and experiment

Experimental Connection • Calculating cross section – Amplitude – Cross section