Gauge Symmetry in Fokker-Planck dynamics

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002naJ221v7911030/hp-pe:hviXraGaugesymmetryinFokker-Planckdynamics
M.deMontignya,b,F.C.Khannab,candA.E.Santanab,d
a
Facult´eSaint-Jean,UniversityofAlberta
8406-91Street,Edmonton,Alberta,CanadaT6C4G9b
TheoreticalPhysicsInstitute,UniversityofAlberta
Edmonton,Alberta,CanadaT6G2J1c
TRIUMF,4004,WesbrookMall
Vancouver,BritishColumbia,CanadaV6T2A3d
InstitutodeF´isica,UniversidadeFederaldaBahiaCampusdeOndina,Salvador,Bahia,Brazil40210-340
February1,2008
Abstract
UsingaGalileanmetricapproach,basedinanembeddingoftheEuclideanspaceintoa(4+1-Minkowskispace,weanalyzeagaugeinvariantLagrangianassociatedwithaRiemannianmanifoldR,withmetricg.Withaspecificchoiceofthegaugecondition,theEuler-LagrangeequationsarewrittencovariantlyinR,andthentheFokker-Planckequationisderived,suchthatthedriftandthediffusiontermsareobtainedfromg.Theanalysisiscarriedoutforboth,abelianandnonabeliansymmetries,andanexamplewiththesu(2symmetryispresented.
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1Introduction
InthispaperweshowthattheFokker-Planckequationcanbederivedviaagaugeinvarianttheory.ThebasicingredientinthederivationisGalileancovariance,whichhasbeenrecentlydevelopedindifferentperspectives,pro-vidingametric,andthusatensor,structurefornonrelativistictheorybasedina4+1Minkowskispace[1,2,3,4,5,6,7,8].Asaconsequence,ageometricunificationofthenonrelativisticandrelativisticphysicsisaccomplished[4,6].Oneinterestingresultisthatthepossibilitytouseideasandconceptsofparticlesphysicsintransporttheory,suchastopologicalterms,symmetrybreaking,gaugesymmetries,andsoon[1,2,9],canbeinvestigatedinasys-tematicandcovariantwayparallelingtherelativisticphysics[4,10].InthiscontextitwouldbeofinteresttoanalyzetypicalstochasticprocessessuchasthosedescribedbytheFokker-Planckdynamics.
TheFokker-PlanckequationisoftenderivedintheanalysisofMarkovprocesses.Fromaphysicalstandpoint,itcanbeintroducedeitherasthedis-tributionofprobabilityversionoftheLangevinequation,describingaclassi-calparticleundertheinfluenceofdissipativeandstochasticforces[11,12,13],orasanapproximationoftheBoltzmannequation[14].Inthislattercase,thecollisiontermisapproximatedtoconsiderthetransitionrate,sayW(p1,k,wherep1=p+k,termsuptothesecondorderink,resultingtheninthedriftandthediffusiontermsoftheFokker-Planckequation[15].Hereweproceedinadifferentway,byanalyzing(firstaU(1gaugeinvariantLa-grangians,inthe(4+1-dimensionMinkowskispace(tobereferredtoasG.Usingasuitablegaugeconditionandaproperdefinitionofeachcomponentforthegaugefield,theEuler-LagrangeequationsresultintheFokker-Planckequation.ThedefinitionofthegaugefieldisbasedontheexistenceofaRie-mannianmanifold,sayR(G,withmetricg,inwhichGistakenasalocalflatspace.Takingthe5-dimensionalequationscovariantlywritteninR(G,thegaugefieldisdefinedwiththeuseofthemetrictensor,whichgivesrisetothedriftanddiffusiontermsoftheFokker-Planckequation.Theanaly-sisoftheconnection,definedbyg,establisheswhetherthediffusiontensorisaconstantornotbyapropercoordinatetransformation.Theseresults,inadditiontoimprovingthestudyofsymmetriesoftheFokker-Plancksys-tems[16],opensthepossibilitytoincludeinthedescriptionofstochasticprocessesnon-abeliangaugesymmetry.Thisaspectisdevelopedherebyus-ing,inparticular,theSU(2gaugesymmetry,followingthemethodsoffieldtheory,ratherthanthegeneralizationofsymplecticstructuresandLiouville
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equation[17].
Thepresentationisorganizedasitfollows.InSectionII,tomakethepresentationselfcontainedandtofixthenotation,abriefoutlineontheGalileicovarianceispresented.TheFokker-Planckequationisderivedfroman-abeliangaugeinvariantLagrangianinSectionIII,andinSectionIVthenon-abeliansituationisaddressed.Finalconcludingandremarksarepre-sentedinSectionV.
2OutlineontheGalileiCovariance
LetusbeginwithabriefoutlineoftheGalileancovariantmethods(formoredetailsseeforinstanceRef.[5,6].LetGbeafivedimensionalmetricspace,withanarbitraryvectordenotedbyx=(x1,x2,x3,x4,x5=(x,x4,x5.TheinnerproductinGisthendefinedby
(x|y=ηµνxµy=

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