arXiv subjects
Publications and source records attributed to A. Di Giacomo.
A detailed discussion is given of the disorder parameter for dual superconductivity of lattice gauge theories, introduced in a previous paper, and of its relation to other approaches. New lattice data are reported. Among other results, we find that the dual superconductivity of compact U(1) is type II.
We determine the topological susceptibility χat T=0 and its behaviour at finite T across the deconfining transition in pure SU(2) gauge theory. We use an improved topological charge density operator. χgoes to zero above T_c, but more slowly than in SU(3) gauge theory.
We survey recent lattice results on QCD topological properties. The behaviour of the topological susceptibility at the deconfining phase transition has been determined. This advance has been made possible by an i) an improvement of the topological charge operator and ii) a non-perturbative determination of renormalizations.
We investigate the performance of the hybrid Monte Carlo algorithm, the standard algorithm used for lattice QCD simulations involving fermions, in updating non-trivial global topological structures. We find that the hybrid Monte Carlo algorithm has serious problems decorrelating the global topological charge at the values of $β$ and $m$ currently simulated, where continuum physics should be approximately realized. This represents a warning which must be seriously considered when simulating full QCD by hybrid Monte Carlo.
We investigate the performance of the hybrid Monte Carlo algorithm in updating non-trivial global topological structures. We find that the hybrid Monte Carlo algorithm has serious problems decorrelating the global topological charge. This represents a warning which must be seriously considered when simulating full QCD, regardless of the number and type of fermions, with this or any similar algorithm. Simulated tempering is examined as a means of accelerating the decorrelation.
A disorder parameter is constructed which signals the condensation of vortices. The construction is tested by numerical simulations on lattice.
We present a measurement of the topological susceptibility in SU(3) Yang-Mills theory through the deconfinement phase transition. An improved operator is used for the topological charge density. A drop by an order of magnitude is observed from the confined to the deconfined phase.
A disorder parameter is constructed which signals the condensation of vortices. The construction is tested by numerical simulations. Advances in the understanding of the basic properties of QCD vacuum will be reported. Three main subjects will be touched: 1) Condensation of monopoles and confinement. 2) Topology, or instanton physics. 3) Gauge invariant field strength correlators, and their behaviour across the deconfining phase transition.
A disorder parameter is constructed which signals the condensation of vortices. The construction is tested by numerical simulations.
We analyze the properties of a class of improved lattice topological charge density operators, constructed by a smearing-like procedure. By optimizing the choice of the parameters introduced in their definition, we find operators having (i) a better statistical behavior as estimators of the topological charge density on the lattice, i.e. less noisy; (ii) a multiplicative renormalization much closer to one; (iii) a large suppression of the perturbative tail (and other unphysical mixings) in the corresponding lattice topological susceptibility.
We review recent results from lattice on topological aspects of QCD: most of the results refer to monopoles and to instantons. We discuss in detail the evidence for condensation of monopoles in the vacuum and confinement of colour by dual superconductivity, and the major role of monopoles in dynamics (monopole dominance). As for instantons we review the $U(1)$ problem, a possible determination of the spin content of the proton, and new lattice data relevant to instanton liquid models.
We analyze the properties of a class of improved lattice topological charge density operators, constructed by a smearing-like procedure. By optimizing the choice of the parameters introduced in their definition, we find operators having (i) a much better statistical behavior as estimators of the topological charge density on the lattice, i.e. much less noisy; (ii) a multiplicative renormalization much closer to one; (iii) a large suppression of the perturbative tail in the corresponding lattice topological susceptibility.
We demonstrate that confinement in $SU(2)$ gauge theory is produced by dual superconductivity of the vacuum. We show that for $T < T_c$ (temperature of deconfining phase transition) the $U(1)$ symmetry related to monopole charge conservation is spontaneously broken; for $T > T_c$ the symmetry is restored.
We study the renormalization group behaviour of the topological charge density in full QCD on the lattice. We propose a way of extracting the necessary renormalization functions from Monte Carlo simulations.
We construct a disorder parameter for dual superconductivity of the ground state of $U(1)$ gauge theory.
We study the behaviour of a suitably defined disorder parameter, showing for the first time monopole condenssation in the ground state of QCD.
We measure field-strength and their correlators in presence of a static $q \bar q$ pair by numerical simulations. We give an interpretation of these data in terms of quadratic and quartic cumulants.
We present preliminary results on the proton spin structure function at zero momentum, in the quenched approximation. Our calculation makes use of a nonperturbative means of determining the multiplicative renormalization of the topological charge density.