Topology and Strings: Topics in N=2N=2

A review on topological strings and the geometry of the space of two dimensional theories. (Lectures given by C. Gomez at the Enrico Fermi Summer School, Varenna, July 1994)Comment: 61 pages, late

Holography and the C-Theorem

We review the geometric definition of C-function in the context of field theories that admit a holographic gravity dual.Comment: Contribution to the proceedings of the TMR 2000 Paris Conferenc

A Note on the String Analog of N=2N=2 Super-Symmetric Yang-Mills

A connection between the conifold locus of the type II string on the $W\:P_{11226}^4$ Calabi-Yau manifold and the geometry of the quantum moduli of $N = 2$ $SU(2)$ super Yang-Mills is presented. This relation is obtained from the anomalous behaviour of the $SU(2)$ super Yang-Mills special coordinates under $S$-duality transformation in $Sl(2;Z) / \Gamma_2$.Comment: 7 pages, Late

The formation of spiral arms and rings in barred galaxies

In this and in a previous paper (Romero-Gomez et al. 2006) we propose a theory to explain the formation of both spirals and rings in barred galaxies using a common dynamical framework. It is based on the orbital motion driven by the unstable equilibrium points of the rotating bar potential. Thus, spirals, rings and pseudo-rings are related to the invariant manifolds associated to the periodic orbits around these equilibrium points. We examine the parameter space of three barred galaxy models and discuss the formation of the different morphological structures according to the properties of the bar model. We also study the influence of the shape of the rotation curve in the outer parts, by making families of models with rising, flat, or falling rotation curves in the outer parts. The differences between spiral and ringed structures arise from differences in the dynamical parameters of the host galaxies. The results presented here will be discussed and compared with observations in a forthcoming paper.Comment: 16 pages, 13 figures, accepted in A&A. High resolution version available at http://www.oamp.fr/dynamique/pap/merce.htm