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We present selected recent results of the QCDSF collaboration on the localization and dimensionality of low overlap eigenmodes and of the topological density in the quenched SU(3) vacuum. We discuss the correlations between the... more
We present selected recent results of the QCDSF collaboration on the localization and dimensionality of low overlap eigenmodes and of the topological density in the quenched SU(3) vacuum. We discuss the correlations between the topological structure revealed by overlap fermions without filtering and the confining monopole and P-vortex structure obtained in the Indirect Maximal Center Gauge.
Overlap fermions are particularly well suited to study the finite temperature dynamics of the chiral symmetry restoration transition of QCD, which might be just an analytic crossover. Using gauge field configurations on a 24^3x10 lattice... more
Overlap fermions are particularly well suited to study the finite temperature dynamics of the chiral symmetry restoration transition of QCD, which might be just an analytic crossover. Using gauge field configurations on a 24^3x10 lattice with N_f=2 flavours of dynamical Wilson-clover quarks generated by the DIK collaboration, we compute the lowest 50 eigenmodes of the overlap Dirac operator and try to locate the transition by fermionic means. We analyse the spectral density, local chirality and localisation properties of the low-lying modes and illustrate the changing topological and (anti-) selfdual structure of the underlying gauge fields across the transition.
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Knowledge of the derivative of the topological susceptibility at zero momentum is important for assessing the validity of the Witten-Veneziano formula for the eta' mass, and likewise for the resolution of the EMC proton spin problem.... more
Knowledge of the derivative of the topological susceptibility at zero momentum is important for assessing the validity of the Witten-Veneziano formula for the eta' mass, and likewise for the resolution of the EMC proton spin problem. We investigate the momentum dependence of the topological susceptibility and its derivative at zero momentum using overlap fermions in quenched lattice QCD simulations. We expose the role of the low-lying Dirac eigenmodes for the topological charge density, and find a negative value for the derivative. While the sign of the derivative is consistent with the QCD sum rule for pure Yang-Mills theory, the absolute value is overestimated if the contribution from higher eigenmodes is ignored.
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The techniques for computing S-matrix elements for nonpolynomial scalar-field Lagrangians with derivative interactions are presented. To second order in the interaction Lagrangian, it is shown that all the dependence arising from the... more
The techniques for computing S-matrix elements for nonpolynomial scalar-field Lagrangians with derivative interactions are presented. To second order in the interaction Lagrangian, it is shown that all the dependence arising from the derivative part is completely separated out as operators acting on integrals identical to those obtained in a nonderivative theory. The Fourier transforms of self-energy graphs for a class of non-local interaction Lagrangians are taken in the massless case. The on-mass-shell contributions are determined by the analytic continuation of the coefficients appearing in the series expansion of the Lagrangian. As special examples, two Lagrangians which are isoscalar analogs of chiral SU(2)×SU(2) Lagrangians are treated. The possible equivalence of on-mass-shell matrix elements for Lagrangians related by nonlinear field transformations is discussed.
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We study the 4-jet and photon plus 3-jet decays of orthoquarkonia, 3S1(QQ)-->GGGG+GGqq-->4 jets, 3S1(QQ-->gammaGGG+gammaGqq-->gamma+3 jets. We show that the characteristic features of the jet distributions in the final state... more
We study the 4-jet and photon plus 3-jet decays of orthoquarkonia, 3S1(QQ)-->GGGG+GGqq-->4 jets, 3S1(QQ-->gammaGGG+gammaGqq-->gamma+3 jets. We show that the characteristic features of the jet distributions in the final state are determined by the 3-gluon vertex of quantum chromodynamics. These decays of a heavy quarkonium resonance (toponium) will offer clear signals for the gluons' self-coupling which can establish QCD as a local non-abelian gauge theory. Kade Foundation Fellow, on leave from Technische Hochschule Aachen.
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We discuss the angular asymmetries of 3-jet events in e + e - annihilation, originating from hard gluon bremsstrahlung off quarks. Lepton beam polarization helps to disentangle the various helicity components of the bremsstrahlung cross... more
We discuss the angular asymmetries of 3-jet events in e + e - annihilation, originating from hard gluon bremsstrahlung off quarks. Lepton beam polarization helps to disentangle the various helicity components of the bremsstrahlung cross section. They are sensitive to the spin of the radiated quantum but are otherwise parameter-free.
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... x, M2), x = lpl/Ipl $2 , then the distribution F (z, M2) of hadrons in reactions (1) is given by 1 1 r(z, M2) = f dxG f dx ô(xxG - z) 0 ... 2. The + e - e G( > 0) M2 change of DG (z, M2) comes from G ->GG and 9+ P-DS (n,... more
... x, M2), x = lpl/Ipl $2 , then the distribution F (z, M2) of hadrons in reactions (1) is given by 1 1 r(z, M2) = f dxG f dx ô(xxG - z) 0 ... 2. The + e - e G( > 0) M2 change of DG (z, M2) comes from G ->GG and 9+ P-DS (n, M2O) G - qq, where the observed hadron comes from a final where ...
A detailed comparison is made between the topological structure of quenched QCD as revealed by the recently proposed over-improved stout-link smearing in conjunction with an improved gluonic definition of the topological density on one... more
A detailed comparison is made between the topological structure of quenched QCD as revealed by the recently proposed over-improved stout-link smearing in conjunction with an improved gluonic definition of the topological density on one hand and a similar analysis made possible by the overlap-fermionic topological charge density both with and without variable ultraviolet cutoff lambdacut. The matching is twofold, provided