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Edward Shuryak

Publications and source records attributed to Edward Shuryak.

173 records · Page 10Linked to original sources
arXiv2000

Implications of the ALEPH tau-Lepton Decay Data for Perturbative and Non-Perturbative QCD

We use ALEPH data on hadronic $τ$ decays in order to calculate Euclidean coordinate space correlation functions in the vector and axial-vector channels. The linear combination $V-A$ receives no perturbative contribution and is quantitatively reproduced by the instanton liquid model. In the case of $V+A$ the instanton calculation is in good agreement with the data once perturbative corrections are included. These corrections clearly show the evolution of $α_s$. We also analyze the range of validity of the Operator Product Expansion (OPE). In the $V-A$ channel we find a dimension $d=6$ contribution which is comparable to the original SVZ estimate, but the instanton model provides a different non-singular term of the same magnitude. In the $V+A$ case both the OPE and the instanton model predict the same $d=4$ power correction induced by the gluon condensate, but it is masked by much larger perturbative contributions. We conclude that the range of validity of the OPE is limited to $x\lsim0.3$ fm, whereas the instanton model describes the data over the entire range.

hep-ph↗
arXiv2000

Instanton-induced Effects in QCD High-Energy Scattering

We evaluate a number of new instanton-induced phenomena in QCD, starting with static dipole-dipole potentials, and proceeding to quark-quark and dipole-dipole scattering at high energy. We use a non-perturbative formulation of the scattering amplitude in terms of a correlator of two Wilson-lines (quarks) or Wilson-loops (dipoles) and analyze the Euclidean amplitudes with both perturbative gluons and instantons. The results are analytically continued to Minkowski geometry, by interpreting the angle between the Wilson lines as rapidity. We discuss the relevance of our results for the phenomenology of near-forward hadronic processes at high energy, especially for processes with multiple color exchanges.

hep-ph↗
arXiv2000

Generalized Mesons in Dense QCD

QCD superconductors in the color-flavor-locked (CFL) phase support excitations (generalized mesons) that can be described as pairs of particles or holes (rather than particle-hole) around a gapped Fermi surface. In weak coupling and to leading logarithm accuracy the scalar and pseudoscalar excitations are massless and the vector and axial-vector excitations are massive and degenerate. The massless scalar excitations are combined with the longitudinal gluons leading to the Meissner effect in the CFL phase. The mass of the composite vector excitations is close to twice the gap in weak coupling, but goes asymptotically to zero with increasing coupling thereby realizing Georgi's vector limit in cold and dense matter. We discuss the possible mixing of the composite scalar and vector excitations with the gluons, their possible coupling to the modified photons and their decay into light pseudoscalars in the CFL phase. The issue of hidden gauge-symmetry in the QCD superconductor is critically examined. The physical implications of our results on soft dilepton and neutrino emission in cold and dense matter are briefly discussed.

hep-ph↗
arXiv1998

Instanton-induced charm contribution to polarized deep-inelastic scattering

Recent data on B decays involving $η'$ may be explained if the singlet axial current of charmed quarks has large matrix element to $η'$, and instantons were shown to be able to generate this effect. We study the magnitude of charm contributions to nucleon polarized structure functions generated in a similar way. Comparing the charm contribution, which is related to a dim(6) gluonic operator, to that of light quarks, which are related by the anomaly equation to $G\tilde G$, we found that $Δc/ΔΣ$ = -(0.2-0.08). Future experiments like COMPASS at CERN identifying charm production in DIS can measure this ``intrinsic polarized charm'' component of the nucleon.

hep-ph↗
arXiv1997

$Ψ'/Ψ$ ratio in Nucleus-Nucleus Collisions : a Measure for the Chiral Symmetry Restoration Temperature ?

We argue that a decrease of the chiral scalar meson mass is responsible for re-creation of $Ψ'$ from $J/Ψ$ in ultrarelativistic nucleus-nucleus collisions. This causes the charmonium yields to freeze out at temperatures close to the chiral symmetry restoration temperature $T_c$. As a result $Ψ'/Ψ$ may serve as a thermometer for $T_c$ itself. Results in a detailed reaction model support the conjecture. They show good agreement with recent data of NA38 and NA50 for $J/Ψ$ and $Ψ'$ production in S on U and Pb on Pb collisions.

hep-ph↗
arXiv1996

Pion electromagnetic formfactor in the instanton vacuum

We have calculated the 3-point correlation function for the electromagnetic interaction of the pion in an ensembles of instantons and anti-instantons, modelling the QCD vacuum. The results are well described by a pion pole and the pion formfactor is extracted, nicely following a standard monopole fit. The experimental data on the formfactor are well reproduced, provided an average instanton size is fixed at ${\barρ}=0.35\pm 0.03\fm$, the same as found for a variety of other correlation functions and was found on the lattice.

hep-ph↗
arXiv1996

Why is a nucleon bound?

In a style of popular article, we discuss models of hadronic structure and their relation with models of the QCD vacuum and lattice simulations. Borrowing two main characters from G.Gamow, Mr.Thompson and Professor, we make a travel in the QCD vacuum. Instanton-generated interaction between quarks appear to be major player, they create quark condensate, constituent quark masses and their bound states with properties very close to those observed. Direct removal of perturbative and confining forces (possible on the lattice by ``cooling'') result in very small modification of hadrons. Phase transitions at high T and large number of quarks in the theory are discussed.

hep-ph↗
arXiv1995

THE QCD VACUUM, CHIRAL PHASE TRANSITION AND QUARK-GLUON PLASMA

In recent years, significant progress was reached in understanding of vacuum and hadronic structure. We review recent works on the {\it point-to-point correlation functions}, comparing those obtained from phenomenology, ``instanton liquid" models and on the lattice. The second topic is physics of chiral symmetry restoration, which may lead to observable hadron modification and unusual event-per-event fluctuations. We discuss collective flow and phenomena related with a remarkable ``softness" of the equation of state near the phase transition, as well as phenomena at small $p_t$. We also describe recent ideas on the mechanism of chiral restoration, based on formation of {\it polarized instanton-antiinstanton molecules}. The third part, related to quark-gluon plasma, is related mainly with the issue of initial equilibration of QGP in high energy collisions. We discuss different ``parton cascade" approaches and argue that {\it multi-gluon} processes dominate them. We briefly discuss predictions for RHIC and LHC energies.

hep-ph↗
arXiv1993

Which chiral symmetry is restored in hot QCD?

We review the current status of the problem of chiral symmetry restoration, discussing an open question of whether at the $SU(N_f)_A$ restoration point $T=T_c$ the $U(1)_A$ chiral symmetry is or is not (approximately) restored. New lattice and instanton-based studies are considered, and some new calculations are suggested to clarify the issue. We also speculate on possible experimental manifestations of two possible scenarios.

hep-ph↗