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1、HomeSearchCollectionsJournalsAboutContactusMyIOPscienceOntreeamplitudesingaugetheoryandgravityThisarticlehasbeendownloadedfromIOPscience.Pleasescrolldowntoseethefulltextarticle.JHEP04(2008)076(http://iopscience.iop.org/1126-6708/2008/04/076)Viewthetableofcontentsforthisissue,orgotothejournalho
2、mepageformoreDownloaddetails:IPAddress:202.141.176.10Thearticlewasdownloadedon25/09/2012at11:46Pleasenotethattermsandconditionsapply.PublishedbyInstituteofPhysicsPublishingforSISSAReceived:February27,2008Accepted:April2,2008Published:April18,2008OntreeamplitudesingaugetheoryandgravityJHEP04(20
3、08)076NimaArkani-HamedaandJaredKaplanabaSchoolofNaturalSciences,InstituteforAdvancedStudy,OldenLane,Princeton,NJ08540,U.S.A.bJeffersonLaboratoryofPhysics,HarvardUniversity,Cambridge,Massachusetts02138,U.S.AE-mail:arkani@ias.edu,jaredk@sns.ias.eduAbstract:TheBCFWrecursionrelationsprovideapowerfu
4、lwaytocomputetreeam-plitudesingaugetheoriesandgravity,butonlyholdifsomeamplitudesvanishwhentwoofthemomentaaretakentoinfinityinaparticularcomplexdirection.Thisisaverysurprisingproperty,sinceindividualFeynmandiagramsalldivergeatinfinitemomentum.Inthispaperwegiveasimplephysicalunderstandingofamplit
5、udesinthislimit,whichcorrespondstoahardparticlewith(complex)light-likemomentummovinginasoftback-ground,andcanbeconvenientlystudiedusingthebackgroundfieldmethodexploitingbackgroundlight-conegauge.Animportantroleisplayedbyenhancedspinsymmetriesatinfinitemomentum-asinglecopyofa“Lorentz”groupforgaug
6、etheoryandtwocopiesforgravity-whichtogetherwithWardidentitiesgiveasystematicexpansionforamplitudesatlargemomentum.Weusethistostudytreeamplitudesinawidevarietyoftheories,andinparticulardemonstratethatcertainpuregaugeandgravityamplitudesdovanishatinfinity.ThustheBCFWrecursionrelationscanbeusedtoc
7、omputecompletelygeneralgluonandgravitontreeamplitudesinanynumberofdimensions.Webrieflycommentontheimplicationsoftheseresultsforcomputingmassive4DamplitudesbyKKreduction,aswellunderstandingtheunexpectedcancelationsthathaverecentlybeenfoun
