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

Implicit-Explicit multistep methods for hyperbolic systems with multiscale relaxation

We consider the development of high order space and time numerical methods based on Implicit-Explicit (IMEX) multistep time integrators for hyperbolic systems with relaxation. More specifically, we consider hyperbolic balance laws in which the convection and the source term may have very different time and space scales. As a consequence the nature of the asymptotic limit changes completely, passing from a hyperbolic to a parabolic system. From the computational point of view, standard numerical methods designed for the fluid-dynamic scaling of hyperbolic systems with relaxation present several drawbacks and typically lose efficiency in describing the parabolic limit regime. In this work, in the context of Implicit-Explicit linear multistep methods we construct high order space-time discretizations which are able to handle all the different scales and to capture the correct asymptotic behavior, independently from its nature, without time step restrictions imposed by the fast scales. Several numerical examples confirm the theoretical analysis

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

Biaxiality in the asymptotic analysis of a 2-D Landau-de Gennes model for liquid crystals

We consider the Landau-de Gennes variational problem on a bound\-ed, two dimensional domain, subject to Dirichlet smooth boundary conditions. We prove that minimizers are maximally biaxial near the singularities, that is, their biaxiality parameter reaches the maximum value $1$. Moreover, we discuss the convergence of minimizers in the vanishing elastic constant limit. Our asymptotic analysis is performed in a general setting, which recovers the Landau-de Gennes problem as a specific case.Comment: 34 pages, 2 figures; typos corrected, minor changes in proofs. Results are unchange

Imagining Village Life in Zambian Fiction

The dualism between the urban and the rural space, and between the systems of social relationships obtaining in each sphere, has proved to be an enduring source of inspiration to African fictional writers since the inception of the genre. Many studies of the genre, however, have failed to recognise the extent to which literary representations of the town and the village have changed over time. Using the case of Zambia, this paper argues that African ideas about the city and the country - and their literary expressions - are historically contingent and rooted in specific socio-economic contexts

A Paradox of Inferentialism

John McDowell articulated a radical criticism of normative inferentialism against Robert Brandom’s expressivist account of conceptual contents. One of his main concerns consists in vindicating a notion of intentionality that could not be reduced to the deontic relations that are established by discursive practitioners. Noticeably, large part of this discussion is focused on empirical knowledge and observational judgments. McDowell argues that there is no role for inference in the application of observational concepts, except the paradoxical one of justifying the content of an observational judgment in terms of itself. This paper examines the semantical consequences of the analysis of the content of empirical judgments in terms of their inferential role. These, it is suggested, are distinct from the epistemological paradoxes that McDowell charges the inferentialist approach with

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