Difference between revisions of "Tree level"

In the context of [[perturbation theory]], a '''tree-level''' [[Feynman diagram]] is a topology contributing to the probability amplitude for a scattering process which contains no closed [[loops]]. If the [[S-matrix]] elements for a process with given initial and final states receive contributions from tree-level diagrams (i.e. the tree-level diagrams are also the lowest order in perturbation theory in which this process is first described), such graphs also constitute the [[leading-order]] diagrams.

In the context of [[perturbation theory]], a '''tree-level''' [[Feynman diagram]] is a topology contributing to the probability amplitude for a scattering process which contains no closed [[loops]]. If the [[S-matrix]] elements for a process with given initial and final states receive contributions from tree-level diagrams (i.e. the tree-level diagrams are also the lowest order in perturbation theory in which this process is first described), such graphs also constitute the [[leading-order]] diagrams.