Semi-analytic calculation of the monopole order parameter in QCD

The monopole order parameter of QCD is computed in terms of gauge invariant field strength correlators. Both quantities are partially known from numerical simulations on the lattice. A new insight results on the structure of the confining vacuum.Comment: Talk presented at QCD06, Montpellier 3-7 July 2006. To appear in the proceeding

Gauge-invariant nonlocal quark condensates in QCD

We study, by numerical simulations on a lattice, the behaviour of the gauge-invariant nonlocal quark condensates in the QCD vacuum both in the quenched approximation and with four flavours of dynamical staggered fermions. The correlation length of the condensate is determined to be roughly twice as big as in the case of the gluon field strength correlators.Comment: LATTICE98(confine

't Hooft tensor for generic gauge group

We study monopoles in gauge theories with generic gauge group. Magnetic charges are in one-to-one correspondence with the second homotopy classes at spatial infinity (${\Pi}_2$), which are therefore identified by the 't Hooft tensor. We determine the 't Hooft tensor in the general case. These issues are relevant to the understanding of Color Confinement.Comment: 5 pages. Contribution to the Conference QCD08, Montpellier 7-12 July 2008 To appear in the proceeding

Condensation of vortices and disorder parameter in 3d Heisenberg model

The 3d Heisenberg model is studied from a dual point of view. It is shown that the disordered phase corresponds to condensation of vortices in the vacuum, and the critical indices are computed from the corresponding disorder parameter.Comment: LATTICE98(spin

Dual superconducting properties of the QCD vacuum

A consistent description of the confining QCD vacuum as a dual superconductor requires a determination of fundamental parameters such as the superconductor correlation length $\xi$ and the field penetration depth $\lambda$, which determine whether the superconductor is of type I or type II. We illustrate preliminary results of a lattice determination of $\xi$ for the case of pure Yang-Mills with two colors, obtained by measuring the temporal correlator of a disorder parameter detecting dual superconductivity.Comment: 4 pages, 2 figures, talk presented at QCD05 (Montpellier) 4-9 July 200

Field strength correlators in QCD at zero and non-zero temperature

We study, by numerical simulations on a lattice, the behaviour of the gauge--invariant field strength correlators in QCD both at zero temperature, down to a distance of 0.1 fm, and at finite temperature, across the deconfinement phase transition.Comment: Talk given at the ``High Energy Conference on Quantum Chromodynamics'', Montpellier (France), 4-12 July 1996 (QCD 96); 5 pages, LaTeX file, uses ``espcrc2.sty''+ 5 PS figure

What is the order of the deconfining phase transition?

The techniques are discussed by which the order of the deconfining phase transition is investigated on the lattice. QCD with $N_f=2$ is a special case, which can provide information on the mechanism of confinement.Comment: Talk at QCD 2003, Montpellier, July 2003, to appear in the proceedings. 4 pages, 1 figur