In physics, a one-loop Feynman diagram is a connectedFeynman diagram with only one cycle (unicyclic). Such a diagram can be obtained from a connected tree diagram by taking two external lines of the same type and joining them together into an edge.
Diagrams with loops (in graph theory, these kinds of loops are called cycles, while the word loop is an edge connecting a vertex with itself) correspond to the quantum corrections to the classical field theory. Because one-loop diagrams only contain one cycle, they express the next-to-classical contributions called the semiclassical contributions.
One-loop diagrams are usually computed as the integral over one independent momentum that can "run in the cycle". The Casimir effect, Hawking radiation and Lamb shift are examples of phenomena whose existence can be implied using one-loop Feynman diagrams, especially the well-known "triangle diagram":
The evaluation of one-loop Feynman diagrams usually leads to divergent expressions, which are either due to:
Infrared divergences are usually dealt with by assigning the zero mass particles a small mass λ, evaluating the corresponding expression and then taking the limit . Ultraviolet divergences are dealt with by renormalization.
loop, feynman, diagram, this, article, does, cite, sources, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, december, 2009, learn, whe. This article does not cite any sources Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources One loop Feynman diagram news newspapers books scholar JSTOR December 2009 Learn how and when to remove this template message In physics a one loop Feynman diagram is a connected Feynman diagram with only one cycle unicyclic Such a diagram can be obtained from a connected tree diagram by taking two external lines of the same type and joining them together into an edge Diagrams with loops in graph theory these kinds of loops are called cycles while the word loop is an edge connecting a vertex with itself correspond to the quantum corrections to the classical field theory Because one loop diagrams only contain one cycle they express the next to classical contributions called the semiclassical contributions One loop diagrams are usually computed as the integral over one independent momentum that can run in the cycle The Casimir effect Hawking radiation and Lamb shift are examples of phenomena whose existence can be implied using one loop Feynman diagrams especially the well known triangle diagram dd The evaluation of one loop Feynman diagrams usually leads to divergent expressions which are either due to zero mass particles in the cycle of the diagram infrared divergence or insufficient falloff of the integrand for high momenta ultraviolet divergence Infrared divergences are usually dealt with by assigning the zero mass particles a small mass l evaluating the corresponding expression and then taking the limit l 0 displaystyle lambda to 0 Ultraviolet divergences are dealt with by renormalization See also EditTadpole physics This quantum mechanics related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title One loop Feynman diagram amp oldid 1042819690, wikipedia, wiki, book, books, library,
