Craig D. Roberts2023年3月10日报告.pdf 
Craig D. Roberts2023年3月10日报告.pdf
NANJING UNIVERSITY Craig Roberts … http://inp.nju.edu.cn/ Grant no. 12135007 Origin of Visible Mass in the Universe Emergence of Mass in the Standard Model How did we get here? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe The Nature of Things ➢ Looking at the known Universe, one could be awed by the many complex things it contains. ➢ Even the Earth itself is complicated enough to generate questions in the minds of we observers ➢ Basic amongst them are those which focus on our own existence and composition. ➢ Here, too, there are many levels to be explored, running right down to the nuclei at the core of every atom and molecule ➢ Even deeper, to the neutrons and protons (nucleons) that constitute those nuclei. ➢ Faced with all this, physicists nevertheless assume that a few simple mathematical rules should be sufficient to provide a complete explanation of everything we can now perceive, and which might become perceptible in future. ➢ This may be correct Or it might be supreme arrogance = hubris Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 3 2023 March 10: USTC - ICTS/PCFT (78) Existence of our Universe depends critically on the following empirical facts: ➢ Proton is massive – i.e., the mass-scale for strong interactions – nucleus formation and nuclear structure – is vastly different to that of atomic physics ➢ Proton is absolutely stable – Despite being a composite object constituted from three valence quarks Emergence: low-level rules producing high-level Neither of these things is evident from just looking at the phenomena, with enormous known/supposed Standard Laws of Nature apparent complexity Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 4 2023 March 10: USTC - ICTS/PCFT (78) Emergentism ➢ One might define emergent phenomena as those features of Nature which don’t readily admit explanation solely in terms of known or conjectured rules. ➢ The concept is at least as old as Aristotle (384-322 BC), who argued that a compound item can have (emergent) properties in the whole which are not explicable merely through the independent actions of the item’s constituent parts. ➢ Aristotle’s view is often represented by the statement: “The whole is more than the sum of its parts”. ➢ In this sense, emergence has its origins in the Greek “sunergos”: “together” plus “working” = origin of our concept of synergy (协同效应), viz. things working together more effectively than could be anticipated from their independent actions in isolation. ➢ This perspective is typically contrasted with that described as Reductionism; namely, the view that everything in Nature can ultimately be viewed as no more complex in principle than, e.g. a (very good) watch, which is clearly a complex object; but, equally clearly, not more than the sum of its parts. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 5 2023 March 10: USTC - ICTS/PCFT (78) Emergentism ➢ One might define emergent phenomena as those features of Nature which don’t readily admit explanation solely in terms of known or conjectured rules. ➢ The concept is at least as old as Aristotle (384-322 BC), who argued that a compound item can have (emergent) properties in the whole which are not explicable merely through the independent actions of the item’s constituent parts. ➢ His view is often represented by the statement: “The whole is more than the sum of its parts”. How does simplicity beget elegant complexity in the emergence of the most fundamental structures in Nature? ➢ In this sense, emergence has its origins in the Greek “sunergos”: “together” plus “working” = origin of our concept of synergy (协同效应), viz. things working together more effectively than could be anticipated from their independent actions in isolation. ➢ This perspective is typically contrasted with that described as Reductionism; namely, the view that everything in Nature can ultimately be viewed as no more complex in principle than, e.g. a (very good) watch, which is clearly a complex object; but, equally clearly, not more than the sum of its parts. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 6 2023 March 10: USTC - ICTS/PCFT (78) Three Great Unifications ✓ “First Great Unification" – Isaac Newton – 350 years ago ✓ Universal Law of Gravitation ✓ Unified the understandings of the observable phenomena of gravity on Earth with the observable behaviour of celestial bodies in space ✓ “Second Great Unification" – 155 years ago – James Clerk Maxwell ✓ Formulated the classical theory of electromagnetic radiation, unifying electricity + magnetism + light as different manifestations of the same phenomenon. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 7 2023 March 10: USTC - ICTS/PCFT (78) Great Unifications ✓ “Third Great Unification" – Standard Model of Particle Physics ✓ 1967 – S. Weinberg “A Model of Leptons” ∼ 13,800 citations ✓ “The most successful theory ever conceived …” ✓ All particles predicted to exist have been found. ✓ The masses of those particles lie within 1% of the theoretical values anticipated by the model. ✓ 55 Nobel Prizes awarded for key developments and discoveries ✓ Description of all known fundamental physics except for gravity, and gravity is something that has no detectable effect when particles are studied a few at a time. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 8 2023 March 10: USTC - ICTS/PCFT (78) 2013: Englert & Higgs ➢ 2012 – Higgs boson discovered at LHC With this discovery the Standard Model of Particle Physics became complete. ➢ 2013 – Nobel Prize in Physics was awarded to Peter Higgs and Francois Englert Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 9 2023 March 10: USTC - ICTS/PCFT (78) 2013: Englert & Higgs ➢ 2012 – Higgs boson discovered at LHC With this discovery the Standard Model of Particle Physics became complete. ➢ 2013 – Nobel Prize in Physics was awarded to Peter Higgs and Francois Englert Where to now? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 10 2023 March 10: USTC - ICTS/PCFT (78) Standard Model of Particle Physics ➢ Standard Model (SM) offers a description of all known fundamental physics except gravity ➢ Gravity has no discernible effect when particles are studied a few at a time. ➢ Since LHC’s discovery of the Higgs in 2012, the Higgs Boson has been promoted to the Centre of Things ➢ Standard Model has 17 particles and 19 parameters, most of which relate to the Higgs and all of which must be determined through comparison with experiment ➢ SM supposedly describes most powerful forces in Nature ➢ Yet, somewhat unsatisfactory Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 11 2023 March 10: USTC - ICTS/PCFT (78) Standard Model of Particle Physics ➢ Strong Interactions in the Standard Model are supposed to be described by quantum chromodynamics (QCD) ➢ Only two parameters are intrinsic to QCD – Higgs enters through current-quark masses ➢ One of them – θQCD – appears to be zero (exactly or almost) … know this because nucleon EDM is (as yet) unmeasurably small ➢ Just one parameter remains to be fixed ➢ Perhaps science has a chance of understanding QCD ∈ SM? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 12 2023 March 10: USTC - ICTS/PCFT (78) ➢ The establishment by the mid-1970’s of QCD as the correct theory of the strong interactions completed what is now known prosaically as the Standard Model. ➢ It offers a description of all known fundamental physics except for gravity, and gravity is something that has no discernible effect when particles are studied a few at a time. ➢ However, the situation is a bit like the way that the Navier-Stokes equation accounts for the flow of water. The equations are at some level obviously correct, but there are only a few, limited circumstances in which their consequences can be worked out in any detail. ➢ Nevertheless, many leading physicists were inclined to conclude in the late 1970’s that the task of basic physics was nearly complete, and we’d soon be out of jobs. ➢ A famous example was the inaugural lecture of Stephen Hawking as Lucasian Professor of Mathematics, a chair first held by Isaac Barrow at Cambridge University. Hawking titled his lecture, “Is the End in Sight for Theoretical Physics?” And he argued strongly for “Yes”. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 13 2023 March 10: USTC - ICTS/PCFT (78) Emergence of Hadron Mass ➢ Standard Model of Particle Physics has one (widely) known mass-generating mechanism = Higgs Boson … impacts are critical to evolution of Universe as we know it ➢ However, Higgs boson is alone responsible for just ∼ 1% of the visible mass in the Universe ➢ Proton mass budget Only 9 MeV/939 MeV is directly from Higgs ➢ Evidently, Nature has another, very effective mechanism for producing mass: Emergent Hadron Mass (EHM) ✓ Alone, it produces 94% of the proton’s mass ✓ Remaining 5% is generated by constructive interference between EHM and Higgs-boson Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 14 2023 March 10: USTC - ICTS/PCFT (78) Emergence of Hadron Mass - Basic Questions ➢ What is the origin of EHM? ➢ Does it lie within the Standard Model, i.e., within QCD ➢ What are the connections with … – Gluon and quark confinement? – Dynamical chiral symmetry breaking (DCSB)? – Nambu-Goldstone modes = π & K? ➢ What is the role of Higgs in modulating observable properties of hadrons? – Critically, without Higgs mechanism of mass generation, π and K would be indistinguishable ➢ Whence mass? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 15 2023 March 10: USTC - ICTS/PCFT (78) Visible Mass ➢ More than 98% of visible mass is contained within nuclei. ➢ First approximation: – atomic weights = sum of the masses of all the nucleons they contain. ➢ Each nucleon has a mass mN ∼ 1 GeV ≈ 2000 me ➢ Higgs boson produces me, but what produces mN = remaining 1999 me? ➢ This question is basic to the whole of modern physics –How can science explain the emergence of hadron mass (EHM)? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 16 2023 March 10: USTC - ICTS/PCFT (78) Origin of Mass: The Frontier of Physics Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe Mass originated 0.000001 second after the Big Bang Its appearance was crucial to the formation of the Universe as we know it Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 18 2023 March 10: USTC - ICTS/PCFT (78) 2013: Englert & Higgs ➢ The most important chapter of the Standard Model is the least understood. ➢ Quantum Chromodynamics (QCD) is supposed to describe all nuclear physics – Matter = quarks – Gauge bosons = gluons ➢ Yet, fifty years after discovery of quarks, we are only just beginning to understand how QCD moulds the basic elements of nuclei: pions, neutrons, protons, etc. ➢ And there are controversies – as theory begins to predict quantities that hitherto were only inferred from measurements via phenomenological fits Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 19 2023 March 10: USTC - ICTS/PCFT (78) Quarks? What are quarks? And what are the gluons that bind them together inside the proton? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe Revolutions in the Early 20th Century ➢ Quantum Mechanics & Special Relativity – Unification encountered many problems ➢ Nonrelativistically, all particles have mass But masslessness is possible in relativistic theories – Einstein’s photon ➢ Antimatter is predicted by relativistic quantum mechanics – Dirac Equation – Antimatter = negative-energy matter … so, for any given system • It costs ZERO energy to create a virtual matter+antimatter pair • or 10 such pairs, or 100 pairs, … or infinitely many! ➢ Quantum mechanics is exactly solvable theory when number of particles is finite ( ∼ 14, with today’s computers and realistic Hamiltonians) ➢ Quantum mechanics is unsolvable when there are infinitely many particles ➢ Relativistic quantum mechanics requires existence of massless particles & antimatter but existence of either destroys relativistic quantum mechanics! Planck Einstein Bohr de Broglie Born Dirac Heisenberg Pauli Schrödinger Feynman Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 21 2023 March 10: USTC - ICTS/PCFT (78) Solving the Problem with Antimatter ➢ There is only one way known to combine quantum mechanics and special relativity Relativistic Quantum Field Theory ➢ 1st example: Electromagnetism – Quantum electrodynamics (QED), 1946-1950 – Feynman, Schwinger, Tomonaga • Nobel Prize (1965): "for their fundamental work in quantum electrodynamics, with deepploughing consequences for the physics of elementary particles". Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 22 2023 March 10: USTC - ICTS/PCFT (78) Solving the Problem with Antimatter ➢ There is only one way known to combine quantum mechanics and special relativity Relativistic Quantum Field Theory ➢ 2nd example: Weak interaction – Radioactive decays, parity-violating decays, electron-neutrino scattering – Glashow, Salam, Weinberg - 1963-1973 • Nobel Prize (1979): 125 • "for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including, inter alia, the prediction of the weak neutral current". Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 23 2023 March 10: USTC - ICTS/PCFT (78) Solving the Problem with Antimatter ➢ 3rd example: Strong interaction … all of nuclear physics and anything made from nuclei = basically everything that we can see and/or touch – Existence and composition of the vast bulk of visible matter in the Universe: • proton, neutron • the forces that form them and bind them into nuclei • responsible for more than 98% of the visible matter in the Universe – Politzer, Gross and Wilczek – 1973-1974 Quantum Chromodynamics – QCD • Nobel Prize (2004): "for the discovery of asymptotic freedom in the theory of the strong interaction". Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 24 2023 March 10: USTC - ICTS/PCFT (78) This is where we live Asymptotic Freedom ⇐ What’s happening out here?! Interaction becomes weaker as energy grows (charges get closer together) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 25 2023 March 10: USTC - ICTS/PCFT Quantum Chromodynamics 𝑎 1 𝑎 𝜆 𝑎 𝑥 +𝜓 ത 𝛾 ⋅ 𝜕𝑥 + 𝑚 + 𝑖𝑔 𝐿 = 𝐺𝜇𝜈 𝑥 𝐺𝜇𝜈 𝛾 ⋅ 𝐴𝑎 𝑥 𝜓 𝑥 4 2 𝑎 𝑥 = 𝜕 𝐴𝑎 (𝑥) − 𝜕 𝐴𝑎 (𝑥) − 𝑓 𝑎𝑏𝑐 𝐴𝑏 (𝑥)𝐴𝑐 (𝑥) 𝐺𝜇𝜈 𝜇 𝜈 𝜈 𝜇 𝜇 𝜈 One line Describes all properties of the bulk of visible matter Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 26 2023 March 10: USTC - ICTS/PCFT (78) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 27 2023 March 10: USTC - ICTS/PCFT (78) Excerpt from the top-10 ➢ Can we quantitatively understand quark and gluon confinement in quantum chromodynamics and the existence of a mass gap? Quantum chromodynamics is the theory describing the strong nuclear force. Carried by gluons, it binds quarks into particles like protons and neutrons. Apparently, the tiny subparticles are permanently confined: one can't pull a quark or a gluon from a proton because the strong force gets stronger with distance and snaps them right back inside. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 28 2023 March 10: USTC - ICTS/PCFT (78) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 29 2023 March 10: USTC - ICTS/PCFT (78) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 30 2023 March 10: USTC - ICTS/PCFT (78) Quantum Chromodynamics 𝑎 1 𝑎 𝜆 𝑎 𝑥 +𝜓 ത 𝛾 ⋅ 𝜕𝑥 + 𝑚 + 𝑖𝑔 𝐿 = 𝐺𝜇𝜈 𝑥 𝐺𝜇𝜈 𝛾 ⋅ 𝐴𝑎 𝑥 𝜓 𝑥 4 2 𝑎 𝑥 = 𝜕 𝐴𝑎 (𝑥) − 𝜕 𝐴𝑎 (𝑥) − 𝑓 𝑎𝑏𝑐 𝐴𝑏 (𝑥)𝐴𝑐 (𝑥) 𝐺𝜇𝜈 𝜇 𝜈 𝜈 𝜇 𝜇 𝜈 ➢ One-line Lagrangian – expressed in terms of gluon and quark partons ➢ Which are NOT the degrees-of-freedom measured in detectors Questions ➢ What are the (asymptotic) detectable degrees-of-freedom? ➢ How are they built from the Lagrangian degrees-of-freedom? ➢ Is QCD really the theory of strong interactions? ➢ Is QCD really a theory? ⇒ Implications far beyond Standard Model Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 31 2023 March 10: USTC - ICTS/PCFT (78) Quantum Chromodynamics ➢ QCD is the first place that humankind has fully experienced the collision between quantum mechanics and special relativity ➢ In attempting to match QCD with Nature, we confront the innumerable complexities of nonperturbative, nonlinear dynamics in relativistic quantum field theory, e.g. – the loss of particle number conservation – the frame and scale dependence of the explanations and interpretations of observable processes – and the evolving character of the relevant degrees-of-freedom ➢ Electroweak theory and phenomena are essentially perturbative, possessing none of this complexity Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 32 2023 March 10: USTC - ICTS/PCFT (78) Strong Interactions in the Standard Model ➢ Only apparent scale in chromodynamics is mass of the quark field ➢ Quark mass is said to be generated by Higgs boson. ➢ In connection with everyday matter, that mass is less-then 0.5% of the empirical scale for strong interactions, viz. more-than two orders-of-magnitude smaller ➢ Plainly, the Higgs-generated mass is very far removed from the natural scale for stronglyinteracting matter ➢ Nuclear physics mass-scale – 1 GeV – is an emergent feature of the Standard Model – No amount of staring at LQCD can reveal that scale ➢ Contrast with quantum electrodynamics, e.g. spectrum of hydrogen levels measured in units of me, which appears in LQED Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 33 2023 March 10: USTC - ICTS/PCFT (78) Whence Mass? ➢ Classical chromodynamics … non-Abelian local gauge theory ➢ Remove the current mass … there’s no energy scale left ➢ No dynamics in a scale-invariant theory; only kinematics … the theory looks the same at all length-scales … there can be no clumps of anything … hence boundstates are impossible. ➢ Our Universe can’t exist ➢ Higgs boson doesn’t solve this problem … – normal matter is constituted from light-quarks – the mass of protons and neutrons, the kernels of all visible matter, are 100-times larger than anything the Higgs can produce ➢ Where did it all begin? … becomes … Where did it all come from? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 34 2023 March 10: USTC - ICTS/PCFT (78) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe Trace Anomaly ➢ In a scale invariant theory the energy-momentum tensor must be traceless: Tμμ ≡ 0 ➢ Regularisation and renormalisation of (ultraviolet) divergences in Quantum Chromodynamics introduces a mass-scale … dimensional transmutation: Lagrangian’s constants (couplings and masses) become dependent on a mass-scale, ζ ➢ α → α(ζ) in QCD’s (massless) Lagrangian density, L(m=0) ⇒ ∂μDμ = δL/δσ = αβ(α) dL/dα = β(α) ¼Gμν Gμν = Tρρ =: Θ0 Trace anomaly QCD β function … specifies how the coupling “runs” Quantisation of renormalisable four-dimensional theory forces nonzero value for trace of energy-momentum tensor Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 36 2023 March 10: USTC - ICTS/PCFT (78) Trace Anomaly ➢ Knowing that a trace anomaly exists does not deliver a great deal … Indicates only that a mass-scale must exist ➢ Key Question: Can one compute and/or understand the magnitude of that scale? ➢ One can certainly measure the magnitude … consider proton: ➢ In the chiral limit the entirety of the proton’s mass is produced by the trace anomaly, Θ0 … In QCD, Θ0 measures the strength of gluon self-interactions The mass of visible matter is … so, from one perspective, almost entirely produced by mp is (somehow) completely generated by glue. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe massless non-matter fields 37 2023 March 10: USTC - ICTS/PCFT (78) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 38 2023 March 10: USTC - ICTS/PCFT (78) Pion ➢ The pion is another one of the hadrons that was discovered as the standard model was being built ➢ Predicted by Yukawa in 1935 – It had to exist, otherwise there was nothing that could hold neutrons and protons together inside a nucleus ➢ The pion, too, is crucial. ➢ It MUST be unnaturally light, otherwise the force it produces would act over a range that is too short to be useful in binding nuclei Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 39 2023 March 10: USTC - ICTS/PCFT (78) Trace Anomaly ➢ In the chiral limit, pion is massless Nambu-Goldstone boson: ⇒ ➢ Does this mean that the scale anomaly vanishes trivially in the pion state, i.e. gluons contribute nothing to the pion mass? ➢ Difficult way to obtain “zero”! ➢ Easier to imagine that “zero” owes to cancellations between different operator contributions to the expectation value of Θ0. ➢ Of course, such precise cancellation should not be an accident. It could only arise naturally because of some symmetry and/or symmetry-breaking pattern. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 40 2023 March 10: USTC - ICTS/PCFT (78) Whence “1” and yet “0” ? ➢No statement of the question “How does the mass of the proton arise?” is complete without the additional clause “How does the pion remain ?” ➢ Natural visible-matter mass-scale must emerge simultaneously with apparent preservation of scale invariance in related systems – Expectation value of Θ0 in pion is always zero, irrespective of the size of the natural mass-scale for strong interactions = mp Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 41 2023 March 10: USTC - ICTS/PCFT (78) Whence “1” and yet “0” ? ➢No statement of the question “How does the mass of the proton arise?” is complete without the additional clause “How does the pion remain ?” ➢ Natural visible-matter mass-scale must emerge simultaneously with apparent Modern Physics must preservation of scale invariance in related systems Elucidate the entire array of Empirical Consequences – Expectation value of Θ0 in pion is always zero, Mechanism responsible irrespective ofof thethe size of the natural mass-scale for strong interactions = mp so that the Standard Model can be Validated Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 42 2023 March 10: USTC - ICTS/PCFT (78) In QCD, so is the absence of mass Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe Particle Data Group Every one of these assertions is wrong Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 45 2023 March 10: USTC - ICTS/PCFT (78) Pinch Technique: Theory and Applications Daniele Binosi & Joannis Papavassiliou Phys. Rept. 479 (2009) 1-152 Gluon self interactions modify the propagation characteristics of the gluon partons that define QCD. They produce dressed gluons with a mathematical connection to the gluon partons, but with wildly different properties. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 46 2023 March 10: USTC - ICTS/PCFT (78) Modern Understanding Grew Slowly from Ancient Origins ➢ More than 40 years ago Dynamical mass generation in continuum quantum chromodynamics, J.M. Cornwall, Phys. Rev. D 26 (1981) 1453 … ∼ 1070 citations 3-gluon vertex ➢ Owing to strong self-interactions, gluon partons ⇒ gluon quasiparticles, described by a mass function that is large at infrared momenta 4-gluon vertex 1 𝑚𝑔2 Gluon propagator … continuum and lattice QCD agree Truly mass from nothing An interacting theory, written in terms of massless gluon fields, ✓ QCD fact produces dressed gluon fields that are characterised by a mass function ✓ Continuum theory and lattice simulations agree that is large at infrared momenta ✓ Empirical verification? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 47 2023 March 10: USTC - ICTS/PCFT (78) Modern Understanding Grew Slowly from Ancient Origins EHM means Gluons are massive ➢ More than 40 years ago Dynamical mass generation in continuum quantum chromodynamics, J.M. Cornwall, Phys. Rev. D 26 (1981) 1453 … ∼ 1050 citations 3-gluon vertex ➢ Owing to strong self-interactions, gluon partons ⇒ gluon quasiparticles, described by a mass function that is large at infrared momenta 1 𝑚𝑔2 Gluon propagator … continuum and lattice QCD agree 4-gluon vertex Truly mass from nothing An interacting theory, written in terms of massless gluon fields, ✓ QCD fact produces dressed gluon fields that are characterised by a mass function ✓ Continuum theory and lattice simulations agree that is large at infrared momenta ✓ Empirical verification? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 48 2023 March 10: USTC - ICTS/PCFT (78) This is where we live Asymptotic Freedom ⇐ What’s happening out here?! Interaction becomes weaker as energy grows (charges get closer together) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 49 2023 March 10: USTC - ICTS/PCFT (78) “Asymptotic freedom comes with a flip side” Perturbative-QCD running coupling extrapolated onto infrared domain k2 < 1 GeV2 o “Imaginatively called infrared slavery” o Coupling runs to infinity as k2 runs to zero o Many people interpret this as being synonymous with confinement o Is this correct? Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 2023 March 10: USTC - ICTS/PCFT (78) 50 W orkshop on Dyson-Schwinger Equations in Modern Mathematics and Physics (DSEMP2014) Trento, Italy, September 22-26, 2014 Process independent effective charge = running coupling Effective charge from lattice QCD, Zhu-Fang Cui, Jin-Li Zhang et al., NJU-INP 014/19, arXiv:1912.08232 [hep-ph], Chin. Phys. C 44 (2020) 083102/1-10 2204 total downloads ➢ Modern theory enables unique QCD analogue of “Gell-Mann – Low” running charge to be rigorously defined and calculated ➢ Analysis of QCD’s gauge sector yields a parameter-free prediction ➢ N.B. Qualitative change in α̂PI(k) at k ≈ ½ mp ➢ No Landau Pole – “Infrared Slavery” picture – linear potential – is not correct explanation of confinement ➢ Below 𝑘 ∼ 𝑚 ෝ 0 , interactions become scale independent, just as they were in the Lagrangian; so, QCD becomes practically conformal again Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe ✓ Process independent strong running coupling Daniele Binosi et al., arXiv:1612.04835 [nucl-th], Phys. Rev. D 96 (2017) 054026/1-7 ✓ Experimental determination of the QCD effective charge αg1(Q). A. Deur; V. Burkert; J.-P. Chen; W. Korsch, Particles 5 (2022) 171 ✓ QCD Running Couplings and Effective Charges, Alexandre Deur, Stanley J. Brodsky and Craig D. Roberts, NJU-INP 071/23, e-Print: 2303.00723 [hep-ph] 51 2023 March 10: USTC - ICTS/PCFT (78) EHM Basics ➢ Absent Higgs boson couplings, the Lagrangian of QCD is scale invariant ➢ Yet … Three pillars – Massless gluons become massive of EHM – A momentum-dependent charge is produced – Massless quarks become massive ➢ EHM is expressed in EVERY strong interaction observable ➢ Challenge to Theory = Elucidate all observable consequences of these phenomena and highlight the paths to measuring them JLab Beam Energy Fraction EHM mapped ➢ Challenge to Experiment = (GeV) (%) Test the theory predictions so that 6 ≈ 35 the boundaries of the Standard Model 12 ≈ 50 can finally be drawn Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 22 ≈ 90 52 2023 March 10: USTC - ICTS/PCFT (78) Focus of experiments at New Generation Facilities Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 53 2023 March 10: USTC - ICTS/PCFT (78) Exposing & Charting EHM ➢ Proton was discovered 100 years ago It is stable; hence, an ideal target in experiments ➢ But just as studying the hydrogen atom ground state didn’t give us QED, focusing on the ground state of only one form of hadron matter will not solve QCD ➢ New Era dawning AMBER @ CERN High energy + high luminosity EIC ⇒ science can move beyond the monomaniacal focus on the proton EicC ➢ Precision studies of the structure of JLab12 & JLab20+ – Nature’s most fundamental Nambu-Goldstone bosons (𝜋 & K) will become possible – Baryon excited states ✓Baryons are the most fundamental three-body systems in Nature ✓If we don’t understand how QCD, a Poincaré-invariant quantum field theory, builds each of the baryons in the complete spectrum, then we don't understand Nature. Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 54 2023 March 10: USTC - ICTS/PCFT (78) Craig Roberts cdroberts@nju.edu.cn 427 Origin of Visible Mass in the Universe 55 2023 March 10: USTC - ICTS/PCFT (78) Wave Functions of Nambu Goldstone Bosons DAs are 1D projection of hadron’s light-front wave function, obtained by integration ∼ 𝑑 2 𝑘⊥ 𝛹(𝑥, 𝑘⊥ ) ➢ Physics Goals: – Pion and kaon distribution amplitudes (DAs – φπ,K) – Nearest thing in quantum field theory to Schrödinger wave function – Consequently, fundamental to understanding π and K structure. ➢ Scientific Context: – For 40 years, the x-dependence of the pion's dominant distribution amplitude (DA) has been controversial. – Modern theory ⇒ EHM expressed in x-dependence of 𝜑𝜋,𝐾 𝑥 – 𝜑𝜋 𝑥 is direct measure of dressed-quark running mass in chiral limit. – Kaon DA = asymmetric around midpoint of its domain of support (0