悼念罗向前教授.ppt

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1、悼念罗向前教授Backtophysics…目前形势和我们的任务－－近年格点QCD进展北京大学物理学院理论物理所刘川Outline格点QCD简介What,Why&How国际上的进展ChiralQuenchingFinitedensityHeavyquarkBroadresonance….我国格点QCD的情况参加的人员已经完成的工作正在进行的工作计算资源总结与展望格点QCD简介WhatislatticeQCDQCD的场变量定义在四维格点上物质场定义在site上规范场定义在link上格点提供了自然的紫外、红外截断规范场部分夸克场部分W

2、hylatticeQCD强相互作用的非微扰特性格点QCD是系统处理QCD非微扰性质的理论方法非微扰的定义（pathintegral）非微扰的计算（MonteCarlo）HowtodolatticeQCDMonteCarlosimulations视为概率密度Quench:略去det格点QCD近年进展格点QCD的几个困难问题ChiralityQuenchedvs.unquenchedFinitedensityHeavyquarkBroadresonance……Allboilsdowntonotenoughcomputers!Thetr

3、oubleofbeingchiralChiralsymmetryiscrucialforQCDNielsen-Ninomiya(no-go)theoremLocalityHermitianCorrectlow-momentumlimitChiral:NOfermionmatrixDcansatisfyalloftheabove4conditionsChiralityBecomesMoreComplicatedonLatticesChiralpropertiesofLQCDdependonThetypeoflatticefermio

4、nbeingusedQuenchedorunquenchedVariantsoflatticefermionsWilsonfermionImprovedWilsonStaggered(Kogut-Susskind)fermionImprovedStaggeredDomainwallfermionOverlapfermionChiralfermionsonthelatticeChiralextrapolation(practicalproblem)Alllatticesimulations(quenchedorunquenched)

5、areperformedataquarkmassvaluehigherthanthatofphysicalu&dquarks.AlllatticeQCDcalculationsinvolvinglightquarksneedchiralextrapolationChiralfermions(morefundamentalproblem)HowtoputchiralfermionsonthelatticeHowtodefinechiralgaugetheorynon-perturbatively,etc.Quenchedvs.unq

6、uenchedQuenchedIgnore(apartfromtrivialrenormalizationeffects)internalquarkloopsGaugefieldconf.generatedviapuregaugePartiallyquenchedGaugefieldconf.generatedatsomeseaquarkmassvaluesValancequarkmassNOTequaltoseaquarkmassUnquenchedJustdon’tquench!Unquenchedconf.sonthemar

7、ket(incomplete)MILCconf.s:Symanzikimprovedgauge(2+1)flavorimprovedstaggered(AsqTad)CP-PACS/JLQCDconf.s:RGimprovedgauge(2+1)flavorCloverquarkRBC&UKQCDconf.s:DBW2improvedgauge2flavordomainwallfermionRunningparametersComparisonsNameCurrentstatusWilsonSimplewell-defined

8、Nochiralsymm.unquenchingcostlyrunningunquenchedStaggeredSimplePartialchiralsymm.UnquenchingnotsocostlyTastedoesNOTtastegood!