On the integrability of Wilson loops in AdS_5 x S^5: Some periodic ansatze

Wilson loops are calculated within the AdS/CFT correspondence by finding a classical solution to the string equations of motion in AdS_5 x S^5 and evaluating its action. An important fact is that this sigma-model used to evaluate the Wilson loops is integrable, a feature that has gained relevance through the study of spinning strings carrying large quantum numbers and spin-chains. We apply the same techniques used to solve the equations for spinning strings to find the minimal surfaces describing a wide class of Wilson loops. We focus on different cases with periodic boundary conditions on the AdS_5 and S^5 factors and find a rich array of solutions. We examine the different phases that appear in the problem and comment on the applicability of integrability to the general problem.Comment: LaTex, 49 pages, 8 figure

Construction and Consequences of Coloured Charges in QCD

This talk reports on work aimed at improving our understanding of charged states in gauge theories.Emphasis is placed on different ways of implementingthe gauge invariance of physical states. QED perturbative calculations are used to stress that gauge invariance is not enough: only a subset of such states have a direct physical significance. In QCD a non-perturbative obstruction means that quarks and gluons cannot form physical states and as such these particles are not truely observables. This sets a fundamental limit on the constituent quark model.Comment: 4 pages, latex, needs sprocl.st

Defect CFTs and holographic multiverse

We investigate some aspects of a recent proposal for a holographic description of the multiverse. Specifically, we focus on the implications on the suggested duality of the fluctuations of a bubble separating two universes with different cosmological constants. We do so by considering a similar problem in a 2+1 CFT with a codimension one defect, obtained by an M5-brane probe embedding in AdS_4x S^7, and studying its spectrum of fluctuations. Our results suggest that the kind of behavior required by the spectrum of bubble fluctuations is not likely to take place in defect CFTs with an AdS dual, although it might be possible if the defect supports a non-unitary theory.Comment: 19 pages; v2: typos fixed, minor changes

A fast and easy approach to the simulation of binary mixtures sorption kinetics

Diffusivity of a component in a binary mixture is affected by the presence of a second component. The knowledge of the influence on each other component diffusivity is very useful for the prediction of sorption kinetics of binary mixtures. In this work kinetic studies of Cr(VI) and Cu(II) binary mixtures sorption onto exhausted coffee encapsulated in calcium alginate beads were carried out in both bench and pilot scale experiments. The spectroscopic analysis evidenced the complexity of the process since different mechanisms such as adsorption, redox reaction and ion exchange are involved. Experimental data were fitted to the Linear Adsorption Model (LAM). An empirical quadratic model was developed to estimate LAM parameters (De) and α = Cf/(Ci − Cf) as a function of the initial concentration of metals in the mixture. The empirical model developed enables to estimate the LAM parameters (De and α) of metal ions binary mixtures provided that the initial concentration of the metal ions is included in the range of concentrations studied. The estimated parameters introduced in LAM equation allow simulating the corresponding binary mixtures sorption kinetics. This study constitutes a fast and easy approach to the modelling of sorption kinetics of complex systems in which different processes take place simultaneously

Exact results for static and radiative fields of a quark in N=4 super Yang-Mills

In this work (which supersedes our previous preprint arXiv:1112.2345) we determine the expectation value of the N=4$ SU(N) SYM Lagrangian density operator in the presence of an infinitely heavy static particle in the symmetric representation of SU(N), by means of a D3-brane probe computation. The result that we obtain coincides with two previous computations of different observables, up to kinematical factors. We argue that these agreements go beyond the D-brane probe approximation, which leads us to propose an exact formula for the expectation value of various operators. In particular, we provide an expression for the total energy loss by radiation of a heavy particle in the fundamental representation.Comment: 14 pages. This submission supersedes our previous preprint arXiv:1112.2345. v2: numerical factors fixed, minor clarifications, added reference