# What is a Witten diagram?

Recently I heard the terminology of Witten diagram. Studying QFT, I frequently see Feynman diagrams and use them to compute scattering amplitudes, one-loop corrections and so on. In string theory courses I often compute string amplitudes with the extended string theory version of Feyman diagrams.

Can you explain to me what "Witten diagram" means? If possible one example would be helpful.

Witten diagram is a diagramatic method to calculate the CFT correlation functions using the bulk information. Say you have a $$\lambda \phi^3$$ interaction in the bulk, you can obtain the $$\langle \mathcal O (\mathbf k_1) \mathcal O (\mathbf k_2) \mathcal O (\mathbf k_3) \rangle$$ CFT correlation function by doing a integration in the bulk AdS spacetime.