On the Four-Dimensional Diluted Ising Model

In this letter we show strong numerical evidence that the four dimensional Diluted Ising Model for a large dilution is not described by the Mean Field exponents. These results suggest the existence of a new fixed point with non-gaussian exponents.Comment: 9 pages. compressed ps-file (uufiles

Matrix model formulation of four dimensional gravity

The attempt of extending to higher dimensions the matrix model formulation of two-dimensional quantum gravity leads to the consideration of higher rank tensor models. We discuss how these models relate to four dimensional quantum gravity and the precise conditions allowing to associate a four-dimensional simplicial manifold to Feynman diagrams of a rank-four tensor model.Comment: Lattice 2000 (Gravity), 4 pages,4 figures, uses espcrc2.st

A Four Dimensional Model of Formal and Informal Learning

Learning systems focused on collaborative learning are often described in terms of formal and informal learning, however definitions of formal and informal learning vary, which makes it difficult to compare systems that may have been described using different perspectives. In this paper we present a framework for describing formality in e-learning systems, which can account for the most common perspectives: formality focused on Learning Objective, Learning Environment, Learning Activity and/or Learning Tool. Our framework can be used to compare different e-learning systems, and can also describe collaborative systems where different students can take very different roles in the activity, and the degree of formality can vary according to the role

Two-particle wave function in four dimensional Ising model

An exploratory study of two-particle wave function is carried out with a four dimensional simple model. The wave functions not only for two-particle ground and first excited states but also for an unstable state are calculated from three- and four-point functions using the diagonalization method suggested by L\"uscher and Wolff. The scattering phase shift is evaluated from these wave functions.Comment: Poster presented at Lattice2004(spectrum), Fermilab, June 21-26, 200

Holographic superconductor in a deformed four-dimensional STU model

In this paper, we consider deformed STU model in four dimensions including both electric and magnetic charges. Using AdS/CFT correspondence, we study holographic superconductor and obtain transport properties like electrical and thermal conductivities. We obtain transport properties in terms of the black hole magnetic charge and interpret it as magnetic monopole of dual field theory. We find that presence of magnetic charge is necessary to have maximum conductivities, and existence of magnetic monopole with a critical charge (137 e) to reach the maximum superconductivity is important. Also, we show that thermal conductivity increases with increasing of magnetic charge. It may be concluded that the origin of superconductivity is magnetic monopole.Comment: 19 pages, 8 Figures. Accepted for publication in EPJ

A WZW model based on a non-semi-simple group

We present a conformal field theory which desribes a homogeneous four dimensional Lorentz-signature space-time. The model is an ungauged WZW model based on a central extension of the Poincar\'e algebra. The central charge of this theory is exactly four, just like four dimensional Minkowski space. The model can be interpreted as a four dimensional monochromatic plane wave. As there are three commuting isometries, other interesting geometries are expected to emerge via $O(3,3)$ duality.Comment: 8 pages, phyzzx, IASSNS-HEP-93/61 Texable versio

One-loop finiteness of the four-dimensional Donaldson-Nair-Schiff non-linear sigma-model

The most general four-dimensional non-linear sigma-model, having the second-order derivatives only and interacting with a background metric and an antisymmetric tensor field, is constructed. Despite its apparent non-renormalizability, just imposing the one-loop UV-finiteness conditions determines the unique model, which may be finite to all orders of the quantum perturbation theory. This model is known as the four-dimensional Donaldson-Nair-Schiff theory, which is a four-dimensional analogue of the standard two-dimensional Wess-Zumino-Novikov-Witten model, and whose unique finiteness properties and an infinite-dimensional current algebra have long been suspected.Comment: 11 pages, LaTeX, macros included; revised versio