The algebra of q-pseudodifferential symbols and the q-W_{KP}^n algebra

In this paper we continue with the program to explore the topography of the space of W-type algebras. In the present case, the starting point is the work of Khesin, Lyubashenko and Roger on the algebra of q-deformed pseudodifferential symbols and their associated integrable hierarchies. The analysis goes on by studying the associated hamiltonian structures for which compact expressions are found. The fundamental Poisson brackets yield q-deformations of W_{KP} and related W-type algebras which, in specific cases, coincide with the ones constructed by Frenkel and Reshetikhin. The construction underlies a continuous correspondence between the hamiltonian structures of the Toda lattice and the KP hierarchies.Comment: 28 pages. Section 5 revised. Misprints corrected. References adde

N=2 supersymmetric Yang-Mills theories and Whitham integrable hierarchies

We review recent work on the study of N=2 super Yang-Mills theory with gauge group SU(N) from the point of view of the Whitham hierarchy, mainly focusing on three main results: (i) We develop a new recursive method to compute the whole instanton expansion of the low-energy effective prepotential; (ii) We interpret the slow times of the hierarchy as additional couplings and promote them to spurion superfields that softly break N=2 supersymmetry down to N=0 through deformations associated to higher Casimir operators of the gauge group; (iii) We show that the Seiberg-Witten-Whitham equations provide a set of non-trivial constraints on the form of the strong coupling expansion in the vicinity of the maximal singularities. We use them to check a proposal that we make for the value of the off-diagonal couplings at those points of the moduli space.Comment: 19 pages, LaTeX, no figures; Invited talk at the Second Meeting "Trends in Theoretical Physics", held in Buenos Aires, December 199

ICT and Economic Growth in Spain 1985-2002

Using new sectoral data on investment and capital services we carry out a growth accounting exercise on Spain 1985-2002. We compute the contribution to output and labour productivity growth of employment, non-ICT and ICT capital, labour qualification and Total Factor Productivity. Results are given for 29 different branches; individually and grouped into four clusters according to their ICT use intensity. Three ICT assets (hardware, communications and software) are considered. We find that although the ICT intensive group appears to be the most dynamic cluster, most of the impact on productivity is still to come. There is some evidence of a reversal of the productivity slow down of the nineties starting in the year 2000.growth accounting, productivity, ICT

Flat tax reforms in the U.S.: A boon for the income poor

In this article we quantify the aggregate, distributional and welfare consequences of two revenue neutral flat-tax reforms using a model economy that replicates the U.S. distributions of earnings, income and wealth in very much detail. We find that the less progressive reform brings about a 2.4 percent increase in steady-state output and a more unequal distribution of after-tax income. In contrast, the more progressive reform brings about a -2.6 percent reduction in steady-state output and a distribution of aftertax income that is more egalitarian. We also find that in the less progressive flat-tax economy aggregate welfare falls by -0.17 percent of consumption, and in the more progressive flat-tax economy it increases by 0.45 percent of consumption. In both flattax reforms the income poor pay less income taxes and obtain sizeable welfare gains

Stability of Charged Global AdS4_4 Spacetimes

We study linear and nonlinear stability of asymptotically AdS$_4$ solutions in Einstein-Maxwell-scalar theory. After summarizing the set of static solutions we first examine thermodynamical stability in the grand canonical ensemble and the phase transitions that occur among them. In the second part of the paper we focus on nonlinear stability in the microcanonical ensemble by evolving radial perturbations numerically. We find hints of an instability corner for vanishingly small perturbations of the same kind as the ones present in the uncharged case. Collapses are avoided, instead, if the charge and mass of the perturbations come to close the line of solitons. Finally we examine the soliton solutions. The linear spectrum of normal modes is not resonant and instability turns on at extrema of the mass curve. Linear stability extends to nonlinear stability up to some threshold for the amplitude of the perturbation. Beyond that, the soliton is destroyed and collapses to a hairy black hole. The relative width of this stability band scales down with the charge Q, and does not survive the blow up limit to a planar geometry.Comment: 43 pg, 22 fig. Published version. Appendix adde

Diffeomorphisms from higher dimensional W-algebras

Classical W-algebras in higher dimensions have been recently constructed. In this letter we show that there is a finitely generated subalgebra which is isomorphic to the algebra of local diffeomorphisms in D dimensions. Moreover, there is a tower of infinitely many fields transforming under this subalgebra as symmetric tensorial one-densities. We also unravel a structure isomorphic to the Schouten symmetric bracket, providing a natural generalization of w_\infty in higher dimensions.Comment: 10 page

Holographic Operator Mixing and Quasinormal Modes on the Brane

We provide a framework for calculating holographic Green's functions from general bilinear actions and fields obeying coupled differential equations in the bulk. The matrix-valued spectral function is shown to be independent of the radial bulk coordinate. Applying this framework we improve the analysis of fluctuations in the D3/D7 system at finite baryon density, where the longitudinal perturbations of the world-volume gauge field couple to the scalar fluctuations of the brane embedding. We compute the spectral function and show how its properties are related to the quasinormal mode spectrum. We study the crossover from the hydrodynamic diffusive to the reactive regime and the movement of quasinormal modes as functions of temperature and density. We also compute their dispersion relations and find that they asymptote to the lightcone for large momenta.Comment: 42 pages, 12 figure