Casimir scaling of SU(3) static potentials

Potentials between static colour sources in eight different representations are computed in four dimensional SU(3) gauge theory. The simulations have been performed with the Wilson action on anisotropic lattices where the renormalised anisotropies have been determined non-perturbatively. After an extrapolation to the continuum limit we are able to exclude any violations of the Casimir scaling hypothesis that exceed 5% for source separations of up to 1 fm.Comment: 12 pages, 10 figures, RevTeX, v2: 1 reference added, more explanation about advantages of anisotrop

On the relevance of center vortices to QCD

In a numerical experiment, we remove center vortices from an ensemble of lattice SU(2) gauge configurations. This removal adds short-range disorder. Nevertheless, we observe long-range order in the modified ensemble: confinement is lost and chiral symmetry is restored (together with trivial topology), proving that center vortices are responsible for both phenomena. As for the Abelian monopoles, they survive but their percolation properties are lost.Comment: 4 pages, 5 figures; discussion expanded, text compressed... to appear in Phys. Rev. Let

Bianchi Type V Viscous Fluid Cosmological Models in Presence of Decaying Vacuum Energy

Bianchi type V viscous fluid cosmological model for barotropic fluid distribution with varying cosmological term $\Lambda$ is investigated. We have examined a cosmological scenario proposing a variation law for Hubble parameter $H$ in the background of homogeneous, anisotropic Bianchi type V space-time. The model isotropizes asymptotically and the presence of shear viscosity accelerates the isotropization. The model describes a unified expansion history of the universe indicating initial decelerating expansion and late time accelerating phase. Cosmological consequences of the model are also discussed.Comment: 10 pages, 3 figure

k-strings and baryon vertices in SU(N) gauge theories

It is pointed out that the sine law for the k-string tension emerges as the critical threshold below which the spatial Z_N symmetry of the static baryon potential is spontaneously broken. This result applies not only to SU(N) gauge theories, but to any gauge system with stable k-strings admitting a baryon vertex made with N sources in the fundamental representation. Some simple examples are worked out.Comment: 4 pages, 4 figures, v2: reference added, v3: comments and references adde

Scaling Study of Pure Gauge Lattice QCD by Monte Carlo Renormalization Group Method

The scaling behavior of pure gauge SU(3) in the region $\beta=5.85 - 7.60$ is examined by a Monte Carlo Renormalization Group analysis. The coupling shifts induced by factor 2 blocking are measured both on 32$^4$ and 16$^4$ lattices with high statistics. A systematic deviation from naive 2-loop scaling is clearly seen. The mean field and effective coupling constant schemes explain part, but not all of the deviation. It can be accounted for by a suitable change of coupling constant, including a correction term ${\cal O}(g^7)$ in the 2-loop lattice $\beta$-function. Based on this improvement, $\sqrt{\sigma}/\Lambda_{\overline {MS}}^{n_f=0}$ is estimated to be $2.2(\pm 0.1)$ from the analysis of the string tension $\sigma$.Comment: 4 pages of A4 format including 7-postscript figure

Quarkonium Suppression

I discuss quarkonium suppression in equilibriated strongly interacting matter. After a brief review of basic features of quarkonium production I discuss the application of recent lattice data on the heavy quark potential to the problem of quarkonium dissociation as well as the problem of direct lattice determination of quarkonium properties in finite temperature lattice QCD.Comment: Invited plenary talk presented on 4th International Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP-2001), November 26-30, 2001, Jaipur; 12 pp, LaTeX, uses pramana.st

Instantons and Monopoles in General Abelian Gauges

A relation between the total instanton number and the quantum-numbers of magnetic monopoles that arise in general Abelian gauges in SU(2) Yang-Mills theory is established. The instanton number is expressed as the sum of the `twists' of all monopoles, where the twist is related to a generalized Hopf invariant. The origin of a stronger relation between instantons and monopoles in the Polyakov gauge is discussed.Comment: 28 pages, 8 figures; comments added to put work into proper contex

The π−\pi-Gluon Exchange Interaction Between Constituent Quarks

The interaction mediated by irreducible pion and gluon exchange between constituent quarks is calculated and shown to have a strong tensor component, which tends to cancel the pion exchange tensor interaction between quarks. Its spin-spin component is somewhat weaker than the pion exchange spin-spin interaction, while its central and spin-orbit components are small in comparison to the corresponding single gluon exchange interactions. The combination of the $\pi-$gluon exchange interaction with the single pion exchange interaction and a weak gluon exchange interaction between constituent quarks has the qualitative features required for understanding the hyperfine splittings of the spectra of the nucleon and the $\Delta$ resonances.Comment: LaTeX, 17 pages, 5 Postscript figure

Instantons in the nonperturbative QCD vacuum

The influence of nonperturbative fields on instantons in quantum chromodynamics is studied. Nonperturbative vacuum is described in terms of nonlocal gauge invariant vacuum averages of gluon field strength.Effective action for instanton is derived in bilocal approximation and it is demonstrated that stochastic background gluon fields are responsible for infra-red (IR) stabilization of instantons. Dependence of characteristic instanton size on gluon condensate and correlation length in nonperturbative vacuum is found. Comparison of obtained instanton size distribution with lattice data is made.Comment: 25 pages, 7 figures, 3 tables, RevTeX4, some corrections made and references adde

Off-diagonal Gluon Mass Generation and Infrared Abelian Dominance in the Maximally Abelian Gauge in Lattice QCD

We study effective mass generation of off-diagonal gluons and infrared abelian dominance in the maximally abelian (MA) gauge. Using the SU(2) lattice QCD, we investigate the propagator and the effective mass of the gluon field in the MA gauge with the U(1)$_3$ Landau gauge fixing. The Monte Carlo simulation is performed on the $12^3 \times 24$ lattice with $2.2 \le \beta \le 2.4$, and also on the $16^4$ and $20^4$ lattices with $2.3 \le \beta \le 2.4$. In the MA gauge, the diagonal gluon component $A_\mu^3$ shows long-range propagation, and infrared abelian dominance is found for the gluon propagator. In the MA gauge, the off-diagonal gluon component $A_\mu^\pm$ behaves as a massive vector boson with the effective mass $M_{\rm off} \simeq 1.2$ GeV in the region of r \gsim 0.2 fm, and its propagation is limited within short range. We conjecture that infrared abelian dominance can be interpreted as infrared inactivity of the off-diagonal gluon due to its large mass generation induced by the MA gauge fixing.Comment: 31 pages, 7 figures and 2 tables included, changed title, corrected typos and updated reference, accepted for publication in Physical Review