FEYNMAN DIAGRAMS HOW TO
Feynman showed how to calculate diagram amplitudes using so-called Feynman rules, which can be derived from the system's underlying Lagrangian. These states can be represented by Feynman diagrams, which are much easier to keep track of than frequently tortuous calculations. The problem of calculating scattering cross sections in particle physics reduces to summing over the amplitudes of all possible intermediate states (each corresponding to one term in the perturbation expansion which is known as the Dyson series). Additionally, only a collection of Feynman diagrams can be said to represent any given particle interaction particles do not choose a particular diagram each time they interact. Feynman diagrams are merely graphs there is no concept of position or space in a Feynman diagram, and there is no concept of time aside from the distinction between incoming and outgoing lines. In some quantum field theories (notably quantum electrodynamics), one can obtain an excellent approximation of the scattering amplitude from a few terms of the perturbative expansion, corresponding to a few simple Feynman diagrams with the same incoming and outgoing lines connected by different vertices and internal lines.įeynman diagrams are frequently confused with spacetime diagrams and bubble chamber images because of their visual similarity, but the connection is weak. Most commonly the bottom of the diagram represents the past and the top of the diagram represents the future.įeynman diagrams are a pictorial representation of a term in a perturbative expansion of the scattering amplitude for the experiment defined by the incoming and outgoing lines.
Lines fall into three categories: internal lines (which connect two vertices), incoming lines (which extend from "the past" to a vertex and represent the initial noninteracting state) and outgoing lines (which extend from a vertex to "the future" and represent the final noninteracting state).
A point where lines connect to other lines is called an interaction vertex, or vertex for short. Particles are represented by lines, which can be drawn in various ways depending on the type of particle being depicted. To appear in the proceedings.A Feynman diagram is a tool invented by American physicist Richard Feynman for performing scattering calculations in quantum field theory. Comment: Invited Talk at Seesaw (1979-2004), Fujihara Seminar, Neutrino mass and Seesaw mechanism, Feb 23-25, 2004, KEK, Japan. We explicitly show that in a class of SUSY SO(10) GUTs there exist cases where LFV and CP violation in B-physics can constitute a major road in simultaneously confirming the ideas of Seesaw and low-energy SUSY. In Grand Unified theories, these effects can be felt even in hadronic physics. Indeed, even when supersymmetry breaking is completely flavour blind, Renormalisation Group running effects are expected to generate large lepton flavour violating entries at the weak scale.
contrary remains unobservable in the SM seesaw. SUSY seesaw exhibits a potentially striking signature: a strong (or even very strong) enhancement of lepton flavour violation (LFV), which on the.
After a quarter of century of intense search for new physics beyond the Standard Model (SM), two ideas stand out to naturally cope with (i) small neutrino masses and (ii) a light higgs boson : Seesaw and SUSY.
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