Download presentation

Presentation is loading. Please wait.

Published byCedric Constance Modified about 1 year ago

1
Rocio BERMUDEZ (U Michoácan); Chen CHEN (ANL, IIT, USTC); Xiomara GUTIERREZ-GUERRERO (U Michoácan); Trang NGUYEN (KSU); Si-xue QIN (PKU); Hannes ROBERTS (ANL, FZJ, UBerkeley); Lei CHANG (ANL, FZJ, PKU); Huan CHEN (BIHEP); Ian CLOËT (UAdelaide); Bruno EL-BENNICH (São Paulo); David WILSON (ANL); Adnan BASHIR (U Michoácan); Stan BRODSKY (SLAC); Gastão KREIN (São Paulo) Roy HOLT (ANL); Mikhail IVANOV (Dubna); Yu-xin LIU (PKU); Robert SHROCK (Stony Brook); Peter TANDY (KSU) Craig Roberts Physics Division Students Early-career scientists Published collaborations: 2010-present

2
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 2

3
Some Relevant References arXiv:1202.2376 arXiv:1202.2376 Confinement contains condensates Stanley J. Brodsky, Craig D. Roberts, Robert Shrock, Peter C. Tandy arXiv:1109.2903 [nucl-th], Phys. Rev. C85 (2012) 012201(RapCom), Expanding the concept of in-hadron condensates Lei Chang, Craig D. Roberts and Peter C. Tandy arXiv:1109.2903 [nucl-th]Phys. Rev. C85 (2012) 012201(RapCom) arXiv:1005.4610 [nucl-th], Phys. Rev. C82 (2010) 022201(RapCom.) arXiv:1005.4610 [nucl-th]Phys. Rev. C82 (2010) 022201(RapCom.) New perspectives on the quark condensate, Brodsky, Roberts, Shrock, Tandy arXiv:0905.1151 [hep-th], PNAS 108, 45 (2011) arXiv:0905.1151 [hep-th]PNAS 108, 45 (2011) Condensates in Quantum Chromodynamics and the Cosmological Constant, Brodsky and Shrock, hep-th/0012253 hep-th/0012253 The Quantum vacuum and the cosmological constant problem, Svend Erik Rugh and Henrik Zinkernagel. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 3

4
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 4

5
Confinement Gluon and Quark Confinement –No coloured states have yet been observed to reach a detector Empirical fact. However –There is no agreed, theoretical definition of light-quark confinement –Static-quark confinement is irrelevant to real-world QCD There are no long-lived, very-massive quarks Confinement entails quark-hadron duality; i.e., that all observable consequences of QCD can, in principle, be computed using an hadronic basis. Craig Roberts: Confinement contains Condensates 5 X SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Colour singlets

6
Confinement Confinement is expressed through a dramatic change in the analytic structure of propagators for coloured particles & can almost be read from a plot of a states’ dressed-propagator –Gribov (1978); Munczek (1983); Stingl (1984); Cahill (1989); Roberts, Williams & Krein (1992); Tandy (1994); … Craig Roberts: Confinement contains Condensates 6 complex-P 2 o Real-axis mass-pole splits, moving into pair(s) of complex conjugate poles or branch points o Spectral density no longer positive semidefinite & hence state cannot exist in observable spectrum Normal particle Confined particle SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs timelike axis: P 2 <0

7
Dressed-gluon propagator Gluon propagator satisfies a Dyson-Schwinger Equation Plausible possibilities for the solution DSE and lattice-QCD agree on the result –Confined gluon –IR-massive but UV-massless –m G ≈ 2-4 Λ QCD Craig Roberts: Confinement contains Condensates 7 perturbative, massless gluon massive, unconfined gluon IR-massive but UV-massless, confined gluon A.C. Aguilar et al., Phys.Rev. D80 (2009) 085018Phys.Rev. D80 (2009) 085018 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

8
DSE Studies – Phenomenology of gluon Wide-ranging study of π & ρ properties Effective coupling –Agrees with pQCD in ultraviolet –Saturates in infrared α(0)/π = 8-15 α(m G 2 )/π = 2-4 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 8 Qin et al., Phys. Rev. C 84 042202(R) (2011)Phys. Rev. C 84 042202(R) (2011) Rainbow-ladder truncation Running gluon mass –Gluon is massless in ultraviolet in agreement with pQCD –Massive in infrared m G (0) = 0.67-0.81 GeV m G (m G 2 ) = 0.53-0.64 GeV

9
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 9

10
Dynamical Chiral Symmetry Breaking SStrong-interaction: Q CD CConfinement –E–Empirical feature –M–Modern theory and lattice-QCD support conjecture that light-quark confinement is a fact associated with violation of reflection positivity; i.e., novel analytic structure for propagators and vertices –S–Still circumstantial, no proof yet of confinement OOn the other hand, DCSB is a fact in QCD –I–It is the most important mass generating mechanism for visible matter in the Universe. Responsible for approximately 98% of the proton’s mass. Higgs mechanism is ( almost ) irrelevant to light-quarks. Craig Roberts: Confinement contains Condensates 10 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

11
Frontiers of Nuclear Science: Theoretical Advances In QCD a quark's effective mass depends on its momentum. The function describing this can be calculated and is depicted here. Numerical simulations of lattice QCD (data, at two different bare masses) have confirmed model predictions (solid curves) that the vast bulk of the constituent mass of a light quark comes from a cloud of gluons that are dragged along by the quark as it propagates. In this way, a quark that appears to be absolutely massless at high energies (m =0, red curve) acquires a large constituent mass at low energies. Craig Roberts: Confinement contains Condensates 11 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs C.D. Roberts, Prog. Part. Nucl. Phys. 61 (2008) 50Prog. Part. Nucl. Phys. 61 (2008) 50 M. Bhagwat & P.C. Tandy, AIP Conf.Proc. 842 (2006) 225-227AIP Conf.Proc. 842 (2006) 225-227

12
Frontiers of Nuclear Science: Theoretical Advances In QCD a quark's effective mass depends on its momentum. The function describing this can be calculated and is depicted here. Numerical simulations of lattice QCD (data, at two different bare masses) have confirmed model predictions (solid curves) that the vast bulk of the constituent mass of a light quark comes from a cloud of gluons that are dragged along by the quark as it propagates. In this way, a quark that appears to be absolutely massless at high energies (m =0, red curve) acquires a large constituent mass at low energies. Craig Roberts: Confinement contains Condensates 12 DSE prediction of DCSB confirmed Mass from nothing! SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

13
12GeV The Future of JLab Numerical simulations of lattice QCD (data, at two different bare masses) have confirmed model predictions (solid curves) that the vast bulk of the constituent mass of a light quark comes from a cloud of gluons that are dragged along by the quark as it propagates. In this way, a quark that appears to be absolutely massless at high energies (m =0, red curve) acquires a large constituent mass at low energies. Craig Roberts: Confinement contains Condensates 13 Jlab 12GeV: Scanned by 2
{
"@context": "http://schema.org",
"@type": "ImageObject",
"contentUrl": "http://images.slideplayer.com/13/4123900/slides/slide_13.jpg",
"name": "12GeV The Future of JLab Numerical simulations of lattice QCD (data, at two different bare masses) have confirmed model predictions (solid curves) that the vast bulk of the constituent mass of a light quark comes from a cloud of gluons that are dragged along by the quark as it propagates.",
"description": "In this way, a quark that appears to be absolutely massless at high energies (m =0, red curve) acquires a large constituent mass at low energies. Craig Roberts: Confinement contains Condensates 13 Jlab 12GeV: Scanned by 2

14
Gluon & quark mass-scales m g (0) and M(0) – dynamically generated mass scales for gluons and quarks – are insensitive to changes in the current- quark mass in the neighbourhood of the physical value SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 14

15
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 15

16
Infinitely many coupled equations: Kernel of the equation for the quark self-energy involves: –D μν (k) – dressed-gluon propagator –Γ ν (q,p) – dressed-quark-gluon vertex each of which satisfies its own DSE, etc… Coupling between equations necessitates a truncation –Weak coupling expansion ⇒ produces every diagram in perturbation theory –Otherwise useless for the nonperturbative problems in which we’re interested Persistent challenge in application of DSEs SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 16 Invaluable check on practical truncation schemes

17
Persistent challenge - truncation scheme Symmetries associated with conservation of vector and axial-vector currents are critical in arriving at a veracious understanding of hadron structure and interactions Example: axial-vector Ward-Takahashi identity –Statement of chiral symmetry and the pattern by which it’s broken in quantum field theory SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 17 Axial-Vector vertex Satisfies an inhomogeneous Bethe-Salpeter equation Quark propagator satisfies a gap equation Kernels of these equations are completely different But they must be intimately related Relationship must be preserved by any truncation Highly nontrivial constraint FAILURE has an extremely high cost – loss of any connection with QCD

18
Persistent challenge - truncation scheme These observations show that symmetries relate the kernel of the gap equation – nominally a one-body problem, with that of the Bethe-Salpeter equation – considered to be a two-body problem Until 1995/1996 people had no idea what to do Equations were truncated, sometimes with good phenomenological results, sometimes with poor results Neither good nor bad could be explained SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 18 quark-antiquark scattering kernel

19
Persistent challenge - truncation scheme Happily, that has changed and there are now two nonperturbative & symmetry preserving truncation schemes 1.1995 – H.J. Munczek, Phys. Rev. D 52 (1995) 4736, Dynamical chiral symmetry breaking, Goldstone’s theorem and the consistency of the Schwinger-Dyson and Bethe-Salpeter EquationsPhys. Rev. D 52 (1995) 4736 1996 – A. Bender, C.D. Roberts and L. von Smekal, Phys.Lett. B 380 (1996) 7, Goldstone Theorem and Diquark Confinement Beyond Rainbow Ladder ApproximationPhys.Lett. B 380 (1996) 7 2.2009 – Lei Chang and C.D. Roberts, Phys. Rev. Lett. 103 (2009) 081601, 0903.5461 [nucl-th], Sketching the Bethe-Salpeter kernelPhys. Rev. Lett. 103 (2009) 081601 0903.5461 [nucl-th] Enables proof of numerous exact results SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 19

20
Dichotomy of the pion Craig Roberts: Confinement contains Condensates 20 How does one make an almost massless particle from two massive constituent-quarks? Naturally, one could always tune a potential in quantum mechanics so that the ground-state is massless – but some are still making this mistake However: current-algebra (1968) This is impossible in quantum mechanics, for which one always finds: SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

21
Dichotomy of the pion Goldstone mode and bound-state The correct understanding of pion observables; e.g. mass, decay constant and form factors, requires an approach to contain a –well-defined and valid chiral limit; –and an accurate realisation of dynamical chiral symmetry breaking. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 21

22
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 22

23
Pion’s Goldberger -Treiman relation Craig Roberts: Confinement contains Condensates 23 Pion’s Bethe-Salpeter amplitude Solution of the Bethe-Salpeter equation Dressed-quark propagator Axial-vector Ward-Takahashi identity entails Pseudovector components necessarily nonzero. Cannot be ignored! Exact in Chiral QCD SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Miracle: two body problem solved, almost completely, once solution of one body problem is known Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

24
Dichotomy of the pion Goldstone mode and bound-state Goldstone’s theorem has a pointwise expression in QCD; Namely, in the chiral limit the wave-function for the two- body bound-state Goldstone mode is intimately connected with, and almost completely specified by, the fully-dressed one-body propagator of its characteristic constituent The one-body momentum is equated with the relative momentum of the two-body system SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 24

25
Dichotomy of the pion Mass Formula for 0 — Mesons Mass-squared of the pseudscalar hadron Sum of the current-quark masses of the constituents; e.g., pion = m u ς + m d ς, where “ς” is the renormalisation point SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 25 Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

26
Dichotomy of the pion Mass Formula for 0 — Mesons Pseudovector projection of the Bethe-Salpeter wave function onto the origin in configuration space –Namely, the pseudoscalar meson’s leptonic decay constant, which is the strong interaction contribution to the strength of the meson’s weak interaction SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 26 Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

27
Dichotomy of the pion Mass Formula for 0 — Mesons Pseudoscalar projection of the Bethe-Salpeter wave function onto the origin in configuration space –Namely, a pseudoscalar analogue of the meson’s leptonic decay constant SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 27 Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

28
Dichotomy of the pion Mass Formula for 0 — Mesons Consider the case of light quarks; namely, m q ≈ 0 –If chiral symmetry is dynamically broken, then f H5 → f H5 0 ≠ 0 ρ H5 → – / f H5 0 ≠ 0 both of which are independent of m q Hence, one arrives at the corollary SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 28 Gell-Mann, Oakes, Renner relation 1968 The so-called “vacuum quark condensate.” More later about this. Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

29
Dichotomy of the pion Mass Formula for 0 — Mesons Consider a different case; namely, one quark mass fixed and the other becoming very large, so that m q /m Q << 1 Then –f H5 ∝ 1/√m H5 –ρ H5 ∝ √m H5 and one arrives at m H5 ∝ m Q SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 29 Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273 Provides QCD proof of potential model result Ivanov, Kalinovsky, Roberts Phys. Rev. D 60, 034018 (1999) [17 pages]

30
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 30

31
Dichotomy of the pion Mass Formula for 0 — Mesons Consider the case of light quarks; namely, m q ≈ 0 –If chiral symmetry is dynamically broken, then f H5 → f H5 0 ≠ 0 ρ H5 → – / f H5 0 ≠ 0 both of which are independent of m q Hence, one arrives at the corollary SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 31 Gell-Mann, Oakes, Renner relation 1968 The so-called “vacuum quark condensate.” More later about this. Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

32
Spontaneous(Dynamical) Chiral Symmetry Breaking The 2008 Nobel Prize in Physics was divided, one half awarded to Yoichiro Nambu "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics" Craig Roberts: Confinement contains Condensates 32 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

33
Nambu – Jona-Lasinio Model Craig Roberts: Confinement contains Condensates 33 Treats a chirally-invariant four-fermion Lagrangian & solves the gap equation in Hartree-Fock approximation (analogous to rainbow truncation) Possibility of dynamical generation of nucleon mass is elucidated Essentially inequivalent vacuum states are identified (Wigner and Nambu states) & demonstration that there are infinitely many, degenerate but distinct Nambu vacua, related by a chiral rotation Nontrivial Vacuum is “Born” SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Dynamical Model of Elementary Particles Based on an Analogy with Superconductivity. I Y. Nambu and G. Jona-Lasinio, Phys. Rev. 122 (1961) 345–358 Dynamical Model Of Elementary Particles Based On An Analogy With Superconductivity. II Y. Nambu, G. Jona-Lasinio, Phys.Rev. 124 (1961) 246-254

34
Gell-Mann – Oakes – Renner Relation Craig Roberts: Confinement contains Condensates 34 This paper derives a relation between m π 2 and the expectation-value, where u o is an operator that is linear in the putative Hamiltonian’s explicit chiral-symmetry breaking term NB. QCD’s current-quarks were not yet invented, so u 0 was not expressed in terms of current-quark fields PCAC-hypothesis (partial conservation of axial current) is used in the derivation Subsequently, the concepts of soft-pion theory Operator expectation values do not change as t=m π 2 → t=0 to take → … in-pion → in-vacuum SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Behavior of current divergences under SU(3) x SU(3). Murray Gell-Mann, R.J. Oakes, B. Renner Phys.Rev. 175 (1968) 2195-2199

35
Gell-Mann – Oakes – Renner Relation Craig Roberts: Confinement contains Condensates 35 PCAC hypothesis; viz., pion field dominates the divergence of the axial-vector current Soft-pion theorem In QCD, this is and one therefore has SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Behavior of current divergences under SU(3) x SU(3). Murray Gell-Mann, R.J. Oakes, B. Renner Phys.Rev. 175 (1968) 2195-2199 Commutator is chiral rotation Therefore, isolates explicit chiral-symmetry breaking term in the putative Hamiltonian Zhou Guangzhao 周光召 Born 1929 Changsha, Hunan province

36
Gell-Mann – Oakes – Renner Relation Craig Roberts: Confinement contains Condensates 36 Theoretical physics at its best. But no one is thinking about how properly to consider or define what will come to be called the vacuum quark condensate So long as the condensate is just a mass-dimensioned constant, which approximates another well-defined matrix element, there is no problem. Problem arises if one over-interprets this number, which textbooks have been doing for a VERY LONG TIME. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs - (0.25GeV) 3

37
Note of Warning Craig Roberts: Confinement contains Condensates 37 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Chiral Magnetism (or Magnetohadrochironics) A. Casher and L. Susskind, Phys. Rev. D9 (1974) 436 These authors argue that dynamical chiral- symmetry breaking can be realised as a property of hadrons, instead of via a nontrivial vacuum exterior to the measurable degrees of freedom The essential ingredient required for a spontaneous symmetry breakdown in a composite system is the existence of a divergent number of constituents – DIS provided evidence for divergent sea of low-momentum partons – parton model.

38
QCD Sum Rules Introduction of the gluon vacuum condensate and development of “sum rules” relating properties of low-lying hadronic states to vacuum condensates Craig Roberts: Confinement contains Condensates 38 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs QCD and Resonance Physics. Sum Rules. M.A. Shifman, A.I. Vainshtein, and V.I. Zakharov Nucl.Phys. B147 (1979) 385-447; citations: 3713

39
QCD Sum Rules Introduction of the gluon vacuum condensate and development of “sum rules” relating properties of low-lying hadronic states to vacuum condensates At this point (1979), the cat was out of the bag: a physical reality was seriously attributed to a plethora of vacuum condensates Craig Roberts: Confinement contains Condensates 39 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs QCD and Resonance Physics. Sum Rules. M.A. Shifman, A.I. Vainshtein, and V.I. Zakharov Nucl.Phys. B147 (1979) 385-447; citations: 3781

40
“quark condensate” 1960-1980 Instantons in non-perturbative QCD vacuum, Instantons in non-perturbative QCD vacuum MA Shifman, AI Vainshtein… - Nuclear Physics B, 1980 Instanton density in a theory with massless quarks, Instanton density in a theory with massless quarks MA Shifman, AI Vainshtein… - Nuclear Physics B, 1980 Exotic new quarks and dynamical symmetry breaking, Exotic new quarks and dynamical symmetry breaking WJ Marciano - Physical Review D, 1980 The pion in QCD The pion in QCD J Finger, JE Mandula… - Physics Letters B, 1980 No references to this phrase before 1980 Craig Roberts: Confinement contains Condensates 40 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

41
Universal Conventions Wikipedia: (http://en.wikipedia.org/wiki/QCD_vacuum)(http://en.wikipedia.org/wiki/QCD_vacuum) “The QCD vacuum is the vacuum state of quantum chromodynamics (QCD). It is an example of a non- perturbative vacuum state, characterized by many non- vanishing condensates such as the gluon condensate or the quark condensate. These condensates characterize the normal phase or the confined phase of quark matter.” SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 41

42
QCDQCD How should one approach this problem, understand it, within Quantum ChromoDynamics? 1)Are the quark and gluon “condensates” theoretically well- defined? 2)Is there a physical meaning to this quantity or is it merely just a mass-dimensioned parameter in a theoretical computation procedure? Craig Roberts: Confinement contains Condensates 42 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs 1973-1974

43
QCDQCD Why does it matter? Craig Roberts: Confinement contains Condensates 43 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs 1973-1974

44
“Dark Energy” Two pieces of evidence for an accelerating universe 1)Observations of type Ia supernovae → the rate of expansion of the Universe is growing 2)Measurements of the composition of the Universe point to a missing energy component with negative pressure: CMB anisotropy measurements indicate that the Universe is at Ω 0 = 1 ⁺⁄₋ 0.04. In a flat Universe, the matter density and energy density must sum to the critical density. However, matter only contributes about ⅓ of the critical density, Ω M = 0.33 ⁺⁄₋ 0.04. Thus, ⅔ of the critical density is missing. Craig Roberts: Confinement contains Condensates 44 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

45
“Dark Energy” In order not to interfere with the formation of structure (by inhibiting the growth of density perturbations) the energy density in this component must change more slowly than matter (so that it was subdominant in the past). Accelerated expansion can be accommodated in General Relativity through the Cosmological Constant, Λ. Einstein introduced the repulsive effect of the cosmological constant in order to balance the attractive gravity of matter so that a static universe was possible. He promptly discarded it after the discovery of the expansion of the Universe. Craig Roberts: Confinement contains Condensates 45 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs In order to have escaped detection, the missing energy must be smoothly distributed. Contemporary cosmological observations mean:

46
“Dark Energy” The only possible covariant form for the energy of the (quantum) vacuum; viz., is mathematically equivalent to the cosmological constant. “It is a perfect fluid and precisely spatially uniform” “Vacuum energy is almost the perfect candidate for dark energy.” Craig Roberts: Confinement contains Condensates 46 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs “The advent of quantum field theory made consideration of the cosmological constant obligatory not optional.” Michael Turner, “Dark Energy and the New Cosmology”

47
“Dark Energy” QCD vacuum contribution If chiral symmetry breaking is expressed in a nonzero expectation value of the quark bilinear, then the energy difference between the symmetric and broken phases is of order M QCD ≈0.3 GeV One obtains therefrom: Craig Roberts: Confinement contains Condensates 47 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs “The biggest embarrassment in theoretical physics.” Mass-scale generated by spacetime-independent condensate Enormous and even greater contribution from Higgs VEV!

48
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 48

49
QCDQCD Are the condensates real? Is there a physical meaning to the vacuum quark condensate (and others)? Or is it merely just a mass-dimensioned parameter in a theoretical computation procedure? Craig Roberts: Confinement contains Condensates 49 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs 1973-1974

50
What is measurable? Craig Roberts: Confinement contains Condensates 50 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs S. Weinberg, Physica 96A (1979) Elements of truth in this perspective

51
Dichotomy of the pion Mass Formula for 0 — Mesons Consider the case of light quarks; namely, m q ≈ 0 –If chiral symmetry is dynamically broken, then f H5 → f H5 0 ≠ 0 ρ H5 → – / f H5 0 ≠ 0 both of which are independent of m q Hence, one arrives at the corollary SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 51 Gell-Mann, Oakes, Renner relation 1968 The so-called “vacuum quark condensate.” More later about this. Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

52
In-meson condensate Craig Roberts: Confinement contains Condensates 52 Maris & Roberts nucl-th/9708029 Pseudoscalar projection of pion’s Bethe-Salpeter wave- function onto the origin in configuration space: |Ψ π PS (0)| – or the pseudoscalar pion-to-vacuum matrix element Rigorously defined in QCD – gauge-independent, cutoff- independent, etc. For arbitrary current-quark masses For any pseudoscalar meson SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs

53
In-meson condensate Craig Roberts: Confinement contains Condensates 53 Pseudovector projection of pion’s Bethe-Salpeter wave- function onto the origin in configuration space: |Ψ π AV (0)| – or the pseudoscalar pion-to-vacuum matrix element – or the pion’s leptonic decay constant Rigorously defined in QCD – gauge-independent, cutoff- independent, etc. For arbitrary current-quark masses For any pseudoscalar meson SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Maris & Roberts nucl-th/9708029

54
In-meson condensate Craig Roberts: Confinement contains Condensates 54 Define Then, using the pion Goldberger-Treiman relations (equivalence of 1- and 2-body problems), one derives, in the chiral limit Namely, the so-called vacuum quark condensate is the chiral-limit value of the in-pion condensate The in-pion condensate is the only well-defined function of current-quark mass in QCD that is smoothly connected to the vacuum quark condensate. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Chiral limit Maris & Roberts nucl-th/9708029 |Ψ π PS (0)|*|Ψ π AV (0)|

55
I.Casher Banks formula: II.Constant in the Operator Product Expansion: III.Trace of the dressed-quark propagator: There is only one condensate Craig Roberts: Confinement contains Condensates 55 SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Langeld, Roberts et al. nucl-th/0301024nucl-th/0301024, Phys.Rev. C67 (2003) 065206 m→0 Density of eigenvalues of Dirac operator Algebraic proof that these are all the same. So, no matter how one chooses to calculate it, one is always calculating the same thing; viz., |Ψ π PS (0)|*|Ψ π AV (0)|

56
Paradigm shift: In-Hadron Condensates Resolution –Whereas it might sometimes be convenient in computational truncation schemes to imagine otherwise, “condensates” do not exist as spacetime-independent mass-scales that fill all spacetime. –So-called vacuum condensates can be understood as a property of hadrons themselves, which is expressed, for example, in their Bethe-Salpeter or light-front wavefunctions. –GMOR cf. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 56 QCDQCD Brodsky, Roberts, Shrock, Tandy, Phys. Rev. C82 (Rapid Comm.) (2010) 022201Phys. Rev. C82 (Rapid Comm.) (2010) 022201 Brodsky and Shrock, PNAS 108, 45 (2011)PNAS 108, 45 (2011)

57
Paradigm shift: In-Hadron Condensates Resolution –Whereas it might sometimes be convenient in computational truncation schemes to imagine otherwise, “condensates” do not exist as spacetime-independent mass-scales that fill all spacetime. –So-called vacuum condensates can be understood as a property of hadrons themselves, which is expressed, for example, in their Bethe-Salpeter or light-front wavefunctions. –No qualitative difference between f π and ρ π SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 57 Brodsky, Roberts, Shrock, Tandy, Phys. Rev. C82 (Rapid Comm.) (2010) 022201Phys. Rev. C82 (Rapid Comm.) (2010) 022201 Brodsky and Shrock, PNAS 108, 45 (2011)PNAS 108, 45 (2011)

58
Paradigm shift: In-Hadron Condensates Resolution –Whereas it might sometimes be convenient in computational truncation schemes to imagine otherwise, “condensates” do not exist as spacetime-independent mass-scales that fill all spacetime. –So-called vacuum condensates can be understood as a property of hadrons themselves, which is expressed, for example, in their Bethe-Salpeter or light-front wavefunctions. –No qualitative difference between f π and ρ π –And SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 58 Chiral limit Brodsky, Roberts, Shrock, Tandy, Phys. Rev. C82 (Rapid Comm.) (2010) 022201Phys. Rev. C82 (Rapid Comm.) (2010) 022201 Brodsky and Shrock, PNAS 108, 45 (2011)PNAS 108, 45 (2011)

59
Topological charge of “vacuum” Wikipedia : Instanton effects are important in understanding the formation of condensates in the vacuum of quantum chromodynamics (QCD)quantum chromodynamics Wikipedia : The difference between the mass of the η and that of the η' is larger than the quark model can naturally explain.quark model This “η-η' puzzle” is resolved by instantons.η-η' puzzleinstantons Claimed that some lattice simulations demonstrate nontrivial topological structures in QCD vacuum Now illustrate new paradigm perspective … SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 59

60
AVWTI ⇒ QCD mass formulae for all pseudoscalar mesons, including those which are charge-neutral Consider the limit of a U(N f )-symmetric mass matrix, then this formula yields: Topological charge density: Q(x) = i(α s /4π) tr C ε μνρσ F μν F ρσ Plainly, the η – η’ mass splitting is nonzero in the chiral limit so long as ν η’ ≠ 0 … viz., so long as the topological content of the η’ is nonzero! Charge-neutral pseudoscalar mesons SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 60 Bhagwat, Chang, Liu, Roberts, Tandy Phys.Rev. C76 (2007) 045203 Algebraic result. Very different than requiring QCD’s vacuum to possess nontrivial topological structure Qualitatively the same as f π, a property of the bound- state

61
Topology and the “condensate” Exact result in QCD, algebraic proof: “chiral condensate” = in-pion condensate the the zeroth moment of a mixed vacuum polarisation –connecting topological charge with the pseudoscalar quark operator SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 61 Bhagwat, Chang, Liu, Roberts, Tandy Phys.Rev. C76 (2007) 045203

62
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 62

63
GMOR Relation Valuable to highlight the precise form of the Gell-Mann–Oakes– Renner (GMOR) relation: Eq. (3.4) in Phys.Rev. 175 (1968) 2195Phys.Rev. 175 (1968) 2195 o m π is the pion’s mass o H χsb is that part of the hadronic Hamiltonian density which explicitly breaks chiral symmetry. Crucial to observe that the operator expectation value in this equation is evaluated between pion states. Moreover, the virtual low-energy limit expressed in the equation is purely formal. It does not describe an achievable empirical situation. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 63 Expanding the concept of in-hadron condensates Lei Chang, Craig D. Roberts and Peter C. Tandy arXiv:1109.2903 [nucl-th], Phys. Rev. C85 (2012) 012201(R) arXiv:1109.2903 [nucl-th]Phys. Rev. C85 (2012) 012201(R)

64
GMOR Relation In terms of QCD quantities, GMOR relation entails o m ud ζ = m u ζ + m d ζ … the current-quark masses o S π ζ (0) is the pion’s scalar form factor at zero momentum transfer, Q 2 =0 RHS is proportional to the pion σ-term Consequently, using the connection between the σ-term and the Feynman-Hellmann theorem, GMOR relation is actually the statement SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 64 Expanding the concept of in-hadron condensates Lei Chang, Craig D. Roberts and Peter C. Tandy arXiv:1109.2903 [nucl-th], Phys. Rev. C85 (2012) 012201(R) arXiv:1109.2903 [nucl-th]Phys. Rev. C85 (2012) 012201(R)

65
GMOR Relation Using it follows that This equation is valid for any values of m u,d, including the neighbourhood of the chiral limit, wherein SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 65 Expanding the concept of in-hadron condensates Lei Chang, Craig D. Roberts and Peter C. Tandy arXiv:1109.2903 [nucl-th], Phys. Rev. C85 (2012) 012201(R) arXiv:1109.2903 [nucl-th]Phys. Rev. C85 (2012) 012201(R) Maris, Roberts and Tandy nucl-th/9707003nucl-th/9707003, Phys.Lett. B420 (1998) 267-273

66
GMOR Relation Consequently, in the neighbourhood of the chiral limit This is a QCD derivation of the commonly recognised form of the GMOR relation. Neither PCAC nor soft-pion theorems were employed in the analysis. Nature of each factor in the expression is abundantly clear; viz., chiral limit values of matrix elements that explicitly involve the hadron. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 66 Expanding the concept of in-hadron condensates Lei Chang, Craig D. Roberts and Peter C. Tandy arXiv:1109.2903 [nucl-th], Phys. Rev. C85 (2012) 012201(R) arXiv:1109.2903 [nucl-th]Phys. Rev. C85 (2012) 012201(R)

67
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 67

68
In-Hadron Condensates Plainly, the in-pseudoscalar-meson condensate can be represented through the pseudoscalar meson’s scalar form factor at zero momentum transfer Q 2 = 0. Using an exact mass formula for scalar mesons, one proves the in-scalar-meson condensate can be represented in precisely the same way. By analogy, and with appeal to demonstrable results of heavy-quark symmetry, the Q 2 = 0 values of vector- and pseudovector-meson scalar form factors also determine the in-hadron condensates in these cases. This expression for the concept of in-hadron quark condensates is readily extended to the case of baryons. Via the Q 2 = 0 value of any hadron’s scalar form factor, one can extract the value for a quark condensate in that hadron which is a reasonable and realistic measure of dynamical chiral symmetry breaking. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 68 Expanding the concept of in-hadron condensates Lei Chang, Craig D. Roberts and Peter C. Tandy arXiv:1109.2903 [nucl-th], Phys. Rev. C85 (2012) 012201(R) arXiv:1109.2903 [nucl-th]Phys. Rev. C85 (2012) 012201(R)

69
Hadron Charges Hadron Form factor matrix elements Scalar charge of a hadron is an intrinsic property of that hadron … no more a property of the vacuum than the hadron’s electric charge, axial charge, tensor charge, etc. … SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 69

70
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 70

71
Confinement Confinement is essential to the validity of the notion of in-hadron condensates. Confinement makes it impossible to construct gluon or quark quasiparticle operators that are nonperturbatively valid. So, although one can define a perturbative (bare) vacuum for QCD, it is impossible to rigorously define a ground state for QCD upon a foundation of gluon and quark quasiparticle operators. Likewise, it is impossible to construct an interacting vacuum – a BCS-like trial state – and hence DCSB in QCD cannot rigorously be expressed via a spacetime-independent coherent state built upon the ground state of perturbative QCD. Whilst this does not prevent one from following this path to build practical models for use in hadron physics phenomenology, it does invalidate any claim that theoretical artifices in such models are empirical. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 71 Confinement Contains Condensates S.J. Brodsky, C.D. Roberts, R. Shrock and P.C. Tandy arXiv:1202.2376 [nucl-th] arXiv:1202.2376 [nucl-th]

72
“ EMPTY space may really be empty. Though quantum theory suggests that a vacuum should be fizzing with particle activity, it turns out that this paradoxical picture of nothingness may not be needed. A calmer view of the vacuum would also help resolve a nagging inconsistency with dark energy, the elusive force thought to be speeding up the expansion of the universe.”dark energy SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 72 “Void that is truly empty solves dark energy puzzle” Rachel Courtland, New Scientist 4 th Sept. 2010 Cosmological Constant: Putting QCD condensates back into hadrons reduces the mismatch between experiment and theory by a factor of 10 46 Possibly by far more, if technicolour-like theories are the correct paradigm for extending the Standard Model Paradigm shift: In-Hadron Condensates

73
SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 73

74
Simulations with static quarks Mean-field picture of gauge-field action – is not observable –Strongly reminiscent of mean-field – bag model – pictures of the nucleon, popular in 80s. Gauge configurations are instanton-like, and instantons have nothing to do with confinement. What is the dynamically generated confinement length-scale in this simulation? –This is not related in any known way to the length-scale imposed on the simulation by choosing a value of the string tension. Infinitely heavy quarks, repositioned by hand. –Natural size of system constituted from infinitely heavy quarks is radius=0 [ r ~ ln M Q /M Q ] –Therefore, no dynamical information present. What is hadron spectrum associated with this simulation? There are no quarks, so is there a quark-hadron duality? –The latter is critical to the new condensate paradigm. Provide simulation results with realistic quark masses, then one can test the new perspective on condensates … present pictures quite likely represent features of hadron interiors. SP, 7-8/05/12: Perspectives in Non-P QCD - 74pgs Craig Roberts: Confinement contains Condensates 74

Similar presentations

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google