资源描述：
《Feynman-Diagram》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。
1、Feynmandiagram1FeynmandiagramFeynmandiagramsareapictorialrepresentationschemeforthemathematicalexpressionsgoverningthebehaviorofsubatomicparticles.Thecalculationofprobabilityamplitudesintheoreticalparticlephysicsrequirestheuseofsomeratherlargeandcomplicatedintegralsoveralargenumberofvariables.The
2、seintegralsdo,however,havearegularstructure,andmayberepresentedgraphicallyasFeynmandiagrams.AFeynmandiagramallowsforasimplevisualizationofwhatwouldotherwisebearatherarcaneandabstractformula.InthisFeynmandiagram,anelectronandapositronannihilate,producingavirtualphotonthatbecomesaquark-antiquarkpai
3、r.Thenoneradiatesagluon.Moreprecisely,aFeynmandiagramisagraphicalrepresentationofaperturbativecontributiontothetransitionamplitudeorcorrelationfunctionofaquantummechanicalorstatisticalfieldtheory.WithinthecanonicalformulationofquantumfieldtheoryaFeynmandiagramrepresentsatermintheWick'sexpansionof
4、theperturbativeS-matrix.Alternatively,thepathintegralformulationofquantumfieldtheoryrepresentsthetransitionamplitudeasaweightedsumofallpossiblehistoriesofthesystemfromtheinitialtothefinalstate,intermsofeitherparticlesorfields.AFeynmandiagramisthenacontributionofaparticularclassofparticlepaths,whi
5、chjoinandsplitasdescribedbythediagram.ThetransitionamplitudeisthengivenasthematrixelementoftheS-matrixbetweentheinitialandthefinalstatesofthequantumsystem.FeynmandiagramsweredevelopedbyRichardFeynman,andarenamedafterhim.Therearemanyapplications,primarilyinquantumfieldtheory,butalsoinotherfields,e
6、.g.,insolid-statetheory.MotivationandhistoryWhencalculatingscatteringcrosssectionsinparticlephysics,theinteractionbetweenparticlescanbedescribedbystartingfromafreefieldwhichdescribestheincomingandoutgoingparticles,andincludinganinteractionHamiltoniantodescribehowtheparticlesdeflectoneanother.Thea
7、mplitudeforscatteringisthesumofeachpossibleinteractionhistoryoverallpossibleInthisdiagram,akaon,madeofanupandanti-strangequark,decaysbothweaklyintermediateparticlestates.Thenumberofandstronglyintothreepions,withinterme
