Topological aspects in non-Abelian gauge theory

We discuss the BRST cohomology and exhibit a connection between the Hodge decomposition theorem and the topological properties of a two dimensional free non-Abelian gauge theory having no interaction with matter fields. The topological nature of this theory is encoded in the vanishing of the Laplacian operator when equations of motion are exploited. We obtain two sets of topological invariants with respect to BRST and co-BRST charges on the two dimensional manifold and show that the Lagrangian density of the theory can be expressed as the sum of terms that are BRST- and co-BRST invariants.Comment: (1+11) pages, LaTeX, no figure

Verso un sistema integrato di documentazione dell’arte rupestre. L’esperienza AKAP (Egitto)

Since 2005 the Aswan-Kom Ombo Archaeological Project (AKAP), managed by Yale and Bologna Universities, has investigated a number of selected areas in the region between Aswan and Kom Ombo. Many of the rock art sites identified within the concession areas are under threat, due to the impact of modern human activities. Three-dimensional technologies, such as digital surveying, laser scanning and photogrammetry, were used for the first time in the Egyptian Nile Valley in order to obtain a highly detailed image of the rock art and its environmental setting. The aim of the project is to improve data recording and analysis while saving economic resources and reducing time in the fieldwork

N=1 Super Yang-Mills on the Lattice in the Strong Coupling Limit

We study the N=1 supersymmetric SU(N) Yang-Mills theory on the lattice at strong coupling. We analyse and discuss the recent results obtained at strong coupling and large N for the mesonic and fermionic propagators and spectrum.Comment: Latex 3 pages. Contribution to the Lattice99 Proceeding

Limits on Lorentz Violation from the Highest Energy Cosmic Rays

We place several new limits on Lorentz violating effects, which can modify particles' dispersion relations, by considering the highest energy cosmic rays observed. Since these are hadrons, this involves considering the partonic content of such cosmic rays. We get a number of bounds on differences in maximum propagation speeds, which are typically bounded at the 10^{-21} level, and on momentum dependent dispersion corrections of the form v = 1 +- p^2/Lambda^2, which typically bound Lambda > 10^{21} GeV, well above the Planck scale. For (CPT violating) dispersion correction of the form v = 1 + p/Lambda, the bounds are up to 15 orders of magnitude beyond the Planck scale.Comment: 24 pages, no figures. Added references, very slight changes. Version published in Physical Review

Two loop effective potential for < A^2_\mu > in the Landau gauge in quantum chromodynamics

We construct the effective potential for the dimension two composite operator 1/2 A^{a 2}_\mu in QCD with massless quarks in the Landau gauge for an arbitrary colour group at two loops. For SU(3) we show that an estimate for the effective gluon mass decreases as N_f increases.Comment: 17 latex page

Numerical study of SU(2) Yang-Mills theory with gluinos

We report on a numerical investigation of the SU(2) gauge theory with gluinos. The low-lying spectrum in bosonic and fermionic channels is determined. Improvements of the multi-bosonic algorithm are discussed.Comment: latex, 3 pages, 4 figures; Poster presented by K. Spanderen at LATTICE9

Screening in Hot SU(2) Gauge Theory and Propagators in 3d Adjoint Higgs model

We investigate the large distance behavior of the electric and magnetic propagators of hot SU(2) gauge theory in different gauges using lattice simulations of the full 4d theory and the effective, dimensionally reduced 3d theory. A comparison of the 3d and 4d data for the propagators suggests that dimensional reduction works surprisingly well down to temperatures T=2 T_c. A detailed study of the volume dependence of magnetic propagators is performed. The electric propagators show exponential decay at large distances in all gauges considered and a possible gauge dependence of the electric screening mass turns out to be statistically insignificant.Comment: Submitted to Proceedings of Lattice 2000 and Workshop "Strong and Electroweak Matter 2000". LaTeX uses espcrc2.st

High Temperature 3D QCD: Dimensional Reduction at Work

We investigate the three-dimensional SU(3) gauge theory at finite temperature in the framework of dimensional reduction. The large scale properties of this theory are expected to be conceptually more complicated than in four dimensions. The dimensionally reduced action is computed in closed analytical form. The resulting effective two-dimensional theory is studied numerically both in the electric and magnetic sector. We find that dimensional reduction works excellently down to temperatures of 1.5 times the deconfinement phase transition temperature and even on rather short length scales. We obtain strong evidence that for ${\rm QCD}_3$, even at high temperature the colour averaged potential is represented by the exchange of a single state, at variance with the usual Debye screening picture involving a pair of electric gluons.Comment: 27 page

Superfield Approach To Nilpotent Symmetries For QED From A Single Restriction: An Alternative To The Horizontality Condition

We derive together the exact local, covariant, continuous and off-shell nilpotent Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST symmetry transformations for the U(1) gauge field (A_\mu), the (anti-)ghost fields ((\bar C)C) and the Dirac fields (\psi, \bar\psi) of the Lagrangian density of a four (3 + 1)-dimensional QED by exploiting a single restriction on the six (4, 2)-dimensional supermanifold. A set of four even spacetime coordinates x^\mu (\mu = 0, 1, 2, 3) and two odd Grassmannian variables \theta and \bar\theta parametrize this six dimensional supermanifold. The new gauge invariant restriction on the above supermanifold owes its origin to the (super) covariant derivatives and their intimate relations with the (super) 2-form curvatures (\tilde F^{(2)})F^{(2)} constructed with the help of (super) 1-form gauge connections (\tilde A^{(1)})A^{(1)} and (super) exterior derivatives (\tilde d)d. The results obtained separately by exploiting (i) the horizontality condition, and (ii) one of its consistent extensions, are shown to be a simple consequence of this new single restriction on the above supermanifold. Thus, our present endeavour provides an alternative to (and, in some sense, generalization of) the horizontality condition of the usual superfield formalism applied to the derivation of BRST symmetries.Comment: LaTeX file, 15 pages, journal-versio

Setting the scale for the Luescher-Weisz action

We study the quark-antiquark potential of quenched SU(3) lattice gauge theory with the Luescher-Weisz action. After blocking the gauge fields with the recently proposed hypercubic transformation we compute the Sommer parameter, extract the lattice spacing a and set the scale at 6 different values of the gauge coupling in a range from a = 0.084 fm to 0.136 fm.Comment: Remarks and references added, to appear in Phys. Rev.