Asymptotic FreedomAsymptotic Freedom-- A Colorful Story for -- A Colorful Story for

Understanding the Strong ForceUnderstanding the Strong Force

Yong-Shi Wu

Center for Advanced Study Tsinghua University (and University of Utah)

(Colloquium on 2004 Nobel Prize of Physics)

The Subatomic WorldThe Subatomic World

向极小尺度推进（ 20 世纪的成就）

原子

原子核

核子

夸克和电子

““ 物质”物质”基本粒子“周期基本粒子“周期表”表”

（每种三色）

（每种无色）

三 代

夸克

轻子

Six Flavors of LeptonsSix Flavors of Leptons

Six Flavors of QuarksSix Flavors of Quarks

Colors of Quarks Colors of Quarks

Why CalledWhy Called CCoolloorrs?s?

There areThere are Three ColorsThree Colors

Equal MixingEqual Mixing leads to (=leads to (=No No CCoolloorr))

Other Properties are Other Properties are NOT NOT AffectedAffected

Dynamical roles? Dynamical roles? UnknownUnknown in in 1960’s1960’s

white

Why Why Three Three ColorsColors ? ?

Puzzle of Quark’s StatisticsPuzzle of Quark’s Statistics

R-ratio in e+e- AnnihilationR-ratio in e+e- Annihilation

Neutral Pion’s Electromagnetic DecayNeutral Pion’s Electromagnetic Decay

Electro-Weak Anomaly CancellationElectro-Weak Anomaly Cancellation

………………………………....

R-ratio in e+e- AnnihilationR-ratio in e+e- Annihilation

四种基本相互作用四种基本相互作用

　引力　　　弱　　　　电磁　　　强

中介粒子

作用于

广义相对论 标准模型 （ Yang-Mills 规范场论）基础理论

四种力的作用范围四种力的作用范围

Properties of Force-Carrying ParticlesProperties of Force-Carrying Particles

Gauge Field PrincipleGauge Field Principle

Symmetry Dictates Interactions (C.N. Yang)

Einstein: General RelativityWeyl: Scale (gauge) InvarinaceFock, London (etc): Phase InvarianceYang-Mills: Non-abelain Generalization of Phase

Gauge fields: Connections, Messengers, Compensating Fields, Fixing Rules for Interactions

Electromagnetic InteractionElectromagnetic Interaction

Weak Interaction in Weak Interaction in Neutron DecayNeutron Decay

(uud)

(udd)

Strong Force between Strong Force between QuarksQuarks

Features of Non-Abelian Gauge FieldsFeatures of Non-Abelian Gauge FieldsGluons carry color charges (color and anti-color)

Quarks Emit Gluon Quarks Emit Gluon and Change their Colorand Change their Color

Color Charge ConservationColor Charge Conservation

Interactions between GluonsInteractions between Gluons

• Three-Gluon Vertex

• Four-Gluon Vertex

Strong Interaction between Strong Interaction between NucleonsNucleons

Nuclear Force as Nuclear Force as Residue Strong ForceResidue Strong Force

Evidence for the Existence of Gluon:Evidence for the Existence of Gluon: Three-Jet Events in e+e- Annihilation Three-Jet Events in e+e- Annihilation

Quark-Antiquark Jets

Quark-Antiquark and Gluon Jets

Two-Jet EventsTwo-Jet Events

夸克的直接证据

Three-Jet EventsThree-Jet Events

胶子的直接证据

Essential Features of QCDEssential Features of QCD(Quantum ChromoDynamics)(Quantum ChromoDynamics)

Quarks with spin-1/2 exist as color tripletsQuarks with spin-1/2 exist as color tripletsGluons with spin-1 exist as color octetGluons with spin-1 exist as color octetCoupling between quarks and gluon existsCoupling between quarks and gluon existsCoupling between 3 (and 4) gluons existsCoupling between 3 (and 4) gluons existsThese couplings are equal.These couplings are equal.These couplings decrease with transferredThese couplings decrease with transferred

momentum as momentum as

(Asymptotic Freedom)(Asymptotic Freedom)

)/ln(/1 22 Q

Pre-history of Asymptotic FreedomPre-history of Asymptotic Freedom

Current Algebra of QuarksCurrent Algebra of Quarks (Gell-Mann, 1965)(Gell-Mann, 1965)

““Nature readsNature reads the book of the book of free field theoryfree field theory.”.”

Pre-history of Asymptotic FreedomPre-history of Asymptotic Freedom

Current Algebra of QuarksCurrent Algebra of Quarks (Gell-Mann, 1965)(Gell-Mann, 1965)

““Nature readsNature reads the book of the book of free field theoryfree field theory.”.”

ScalingScaling in in Deep Inelastic ScatteringDeep Inelastic Scattering (Bjorken,1967)(Bjorken,1967)

Pre-history of Asymptotic FreedomPre-history of Asymptotic Freedom

Current Algebra of QuarksCurrent Algebra of Quarks (Gell-Mann, 1965)(Gell-Mann, 1965)

““Nature readsNature reads the book of the book of free field theoryfree field theory.”.”

ScalingScaling in in Deep Inelastic ScatteringDeep Inelastic Scattering (Bjorken,1967)(Bjorken,1967)

Parton Model for ProtonParton Model for Proton (Feynman, 1969)(Feynman, 1969)

Partons behavePartons behave like masslesslike massless free free particlesparticles

Pre-history of Asymptotic FreedomPre-history of Asymptotic Freedom

Current Algebra of QuarksCurrent Algebra of Quarks (Gell-Mann, 1965)(Gell-Mann, 1965)

““Nature readsNature reads the book of the book of free field theoryfree field theory.”.”

ScalingScaling in in Deep Inelastic ScatteringDeep Inelastic Scattering (Bjorken,1967)(Bjorken,1967)

Parton Model for ProtonParton Model for Proton (Feynman, 1969)(Feynman, 1969)

Partons behavePartons behave like masslesslike massless free free particlesparticles

RenormalizationRenormalization Group Equation Group Equation

((Symannzik 1971, Callan 1972)Symannzik 1971, Callan 1972)

In In quantum fieldquantum field theorytheory, , to getto get Bjorken scalingBjorken scaling

needs aneeds a runningrunning coupling constant with acoupling constant with a

negativenegative slope (as momentum increases)slope (as momentum increases)

Deep Inelastic ScatteringDeep Inelastic Scattering

Observation of ScalingObservation of Scaling

Quark and Gluon PropagatorsQuark and Gluon Propagators

Gluon CouplingsGluon Couplings

One-Loop Propagator DiagramsOne-Loop Propagator Diagrams

One-Loop Vertex DiagramsOne-Loop Vertex Diagrams

Negative Negative ββ- Function- Function

Experimental ConfirmationExperimental Confirmationof Asymptotic Freedomof Asymptotic Freedom

QCD Corrections to Scaling LawQCD Corrections to Scaling Law

Color ConfinementColor Confinement渐近（紫外，即高能量、小距离）自由渐近（紫外，即高能量、小距离）自由的另一面的另一面 就是红外奴役，即低能量、大距离作用很强。就是红外奴役，即低能量、大距离作用很强。

这导致颜色囚禁：仅颜色中性态出现在低能谱。这导致颜色囚禁：仅颜色中性态出现在低能谱。单个夸克态和单个胶子态，都不能在低能看见单个夸克态和单个胶子态，都不能在低能看见。。

Color ConfinementColor Confinement

规范场规范场粒子质量的佯谬有了粒子质量的佯谬有了一个一个满意的答案满意的答案。。 （（ It took 20 years to resolve the paradox!)It took 20 years to resolve the paradox!)重子物质重子物质质量的起源：质量的起源： 被囚禁的夸克、胶子的动能被囚禁的夸克、胶子的动能。。

QCDQCD 中中颜色囚禁的机理颜色囚禁的机理尚未完全了解尚未完全了解。。

Unification of Coupling ConstantsUnification of Coupling Constants

supporting low-energy supersymmetry breaking !

粒子物理标准模型是粒子物理标准模型是现代物理学的伟大成就现代物理学的伟大成就

Special Theory of Relativity (Einstein)Special Theory of Relativity (Einstein)

Quantum Theory (Bohr, Heisenberg, Quantum Theory (Bohr, Heisenberg,

SchrSchröödinger, Dirac, Fermi)dinger, Dirac, Fermi)

Quantum Electrodynamics (Feynman, Quantum Electrodynamics (Feynman,

Schwinger, Tomonaga, Schwinger, Tomonaga, DysonDyson))

Gauge Field Principle (Yang, Gauge Field Principle (Yang, MillsMills))

Quantum Flavodynamics (Glashow, Quantum Flavodynamics (Glashow,

Weinberg, Salam, Veltman, ‘t Hooft)Weinberg, Salam, Veltman, ‘t Hooft)

Quantum Chromodynamics Quantum Chromodynamics

新的征途，新的挑战新的征途，新的挑战

当代物理学四大前沿当代物理学四大前沿

• 量子操作和新器件材料： 原子电子和光量子态操作、纳米结构、自旋电子学　　 量子信息、量子计算、量子通讯、．．．• 复杂系统：　　量子多体系统、新物态、非平衡系统、湍流、　　 生物物理、地球物理、高密度系统、．．．• 宇宙的结构与演化：　　观测新窗口（微波、 X 射线、 γ 射线、中微子、引力波）　　 传统和粒子天体物理、宇宙学与黑洞、暗能量、暗物质．．．• 基本定律与对称性：　　标准模型、超对称、大统一、多维、量子引力、弦论 ．．．　

73%

23%

Known

Unknown

结束语结束语现代物理学的辉煌成就让我们感到骄傲。现代物理学的辉煌成就让我们感到骄傲。

当前物理学前沿的全面挑战使我们振奋。当前物理学前沿的全面挑战使我们振奋。

物理学在纳米、新材料、新物态、量子物理学在纳米、新材料、新物态、量子 信息、 生物等领域的新突破将给人类信息、 生物等领域的新突破将给人类 社会和生活带来更深刻的变化。社会和生活带来更深刻的变化。

物理学基础理论新革命的曙光就在前头。物理学基础理论新革命的曙光就在前头。

Thank you Thank you

for Your Patience for Your Patience