Graphical and Kinematical Approach to Cosmological Horizons

We study the apparition of event horizons in accelerated expanding cosmologies. We give a graphical and analytical representation of the horizons using proper distances to coordinate the events. Our analysis is mainly kinematical. We show that, independently of the dynamical equations, all the event horizons tend in the future infinity to a given expression depending on the scale factor that we call asymptotic horizon. We also encounter a subclass of accelerating models without horizon. When the ingoing null geodesics do not change concavity in its cosmic evolution we recover the de Sitter and quintessence-Friedmann-Robertson-Walker models.Comment: Latex2e, 27 pages, 4 figures, submitted to Class. Quantum Gra

Comparative Study: The Ethnoarchaeology of Corral Abandonment in the Famorca District

Reproduced with permission of the publisher. © Authors and School of Archaeology and Ancient History, University of Leicester, 2004. Details of the full publication are available at: http://www.le.ac.uk/ar/research/pubs/catalogue.htm

Post-abandonment corral sequences

Reproduced with permission of the publisher

Case Study II: VG4 - Building and Land Use

Reproduced with permission of the publisher. © Authors and School of Archaeology and Ancient History, University of Leicester, 2004. Details of the full publication are available at: http://www.le.ac.uk/ar/research/pubs/catalogue.htm

Brane Realizations of Quantum Hall Solitons and Kac-Moody Lie Algebras

Using quiver gauge theories in (1+2)-dimensions, we give brane realizations of a class of Quantum Hall Solitons (QHS) embedded in Type IIA superstring on the ALE spaces with exotic singularities. These systems are obtained by considering two sets of wrapped D4-branes on 2-spheres. The space-time on which the QHS live is identified with the world-volume of D4-branes wrapped on a collection of intersecting 2-spheres arranged as extended Dynkin diagrams of Kac-Moody Lie algebras. The magnetic source is given by an extra orthogonal D4-brane wrapping a generic 2-cycle in the ALE spaces. It is shown as well that data on the representations of Kac-Moody Lie algebras fix the filling factor of the QHS. In case of finite Dynkin diagrams, we recover results on QHS with integer and fractional filling factors known in the literature. In case of hyperbolic bilayer models, we obtain amongst others filling factors describing holes in the graphene.Comment: Lqtex; 15 page

On F-theory Quiver Models and Kac-Moody Algebras

We discuss quiver gauge models with bi-fundamental and fundamental matter obtained from F-theory compactified on ALE spaces over a four dimensional base space. We focus on the base geometry which consists of intersecting F0=CP1xCP1 Hirzebruch complex surfaces arranged as Dynkin graphs classified by three kinds of Kac-Moody (KM) algebras: ordinary, i.e finite dimensional, affine and indefinite, in particular hyperbolic. We interpret the equations defining these three classes of generalized Lie algebras as the anomaly cancelation condition of the corresponding N =1 F-theory quivers in four dimensions. We analyze in some detail hyperbolic geometries obtained from the affine A base geometry by adding a node, and we find that it can be used to incorporate fundamental fields to a product of SU-type gauge groups and fields.Comment: 13 pages; new equations added in section 3, one reference added and typos correcte