N=2 four-dimensional gauge theories from fractional branes

This is a pedagogical and extended version of the results published in Refs. [1,2] and presented by the authors in various talks during the last year. We discuss the type II D-branes (both regular and fractional) of the orbifold R^{1,5}*R^4/Z_2, we determine their corresponding supergravity solution and show how this can be used to study the properties of N=2 super Yang-Mills. Supergravity is able to reproduce the perturbative moduli space of the gauge theory, while it does not encode the non-perturbative corrections. The short distance region of space-time, which corresponds to the infrared region of the gauge theory, is excised by an enhancon mechanism, and more states should be included in the low energy effective action in order to enter inside the enhancon and recover the instanton corrections. (To be published on a Memorial Volume commemorating Michael Marinov)Comment: 44 pages, AMS-LaTeX, no figure

Fractional Branes and N=1 Gauge Theories

We discuss fractional D3-branes on the orbifold C^3/Z_2*Z_2. We study the open and the closed string spectrum on this orbifold. The corresponding N=1 theory on the brane has, generically, a U(N_1)*U(N_2)*U(N_3)*U(N_4) gauge group with matter in the bifundamental. In particular, when only one type of brane is present, one obtains pure N=1 Yang-Mills. We study the coupling of the branes to the bulk fields and present the corresponding supergravity solution, valid at large distances. By using a probe analysis, we are able to obtain the Wilsonian beta-function for those gauge theories that possess some chiral multiplet. Although, due to the lack of moduli, the probe technique is not directly applicable to the case of pure N=1 Yang-Mills, we point out that the same formula gives the correct result also for this case.Comment: 21 pages, AMS-LaTeX, v2: references added and typos correcte

Gauge theory renormalizations from the open bosonic string

We present a unified point of view on the different methods available in the literature to extract gauge theory renormalization constants from the low-energy limit of string theory. The Bern-Kosower method, based on an off-shell continuation of string theory amplitudes, and the construction of low-energy string theory effective actions for gauge particles, can both be understood in terms of strings interacting with background gauge fields, and thus reproduce, in the low-energy limit, the field theory results of the background field method. We present in particular a consistent off-shell continuation of the one-loop gluon amplitudes in the open bosonic string that reproduces exactly the results of the background field method in the Feynman gauge.Comment: 14 pages, latex, no figure

Multicultural places and the idea of home

Place identification in urban sociology has traditionally be associated with a sense of &lsquo;being at home&rsquo; and connected to the formation of stable and fixed identities. The rise in transnational migration and the increasing number of refugees around the world has made particular regions and communities, within many western nations, culturally diverse. This has led to a re-conceptualisation and re-examination of the relationship between place and home. In light of this new paradigm I explore the existence of multicultural places and investigate the ways, if any, we can speak of &lsquo;being at home&rsquo; in these diverse urban places. If home has been traditionally associated with order, sameness and identity while multicultural places are conceptualised in terms of fluidity, contingency, heterogeneity and difference then there seems to be an inherent tension between these two ideas. Are the ideas of home and multiculturalism mutually exclusive? I maintain that they are dialectically interwoven, especially when we acknowledge that otherness and home should not be conceived in binary terms. In order to examine this complex relationship the paper provides a brief discussion of home within the discourses of modernity and postmodernity and then links these discourses to phenomenological and sociological approaches to home. The concluding section demonstrates how home and otherness are expressed in intercultural moments where sameness and diversity rub against each other causing occasional friction but also moments of intercultural dialogue.<br /

New Results on the Phase Diagram of the FFXY Model: A Twisted CFT Approach

The issue of the number, nature and sequence of phase transitions in the fully frustrated XY (FFXY) model is a highly non trivial one due to the complex interplay between its continuous and discrete degrees of freedom. In this contribution we attack such a problem by means of a twisted conformal field theory (CFT) approach and show how it gives rise to the U (1)$\otimes Z_{2}$ symmetry and to the whole spectrum of excitations of the FFXY model.Comment: 7 pages; talk given by G. Niccoli at "Path Integrals - New Trends and Perspectives International Conference", Max-Planck-Institut, Dresden, Germany, September 23 - 28, 200

Anomalies and Tadpoles in Open/Closed String Duality

We discuss the role played by the divergences appearing in the interaction between a fractional D3 brane dressed with an SU(N) gauge field and a stack of N fractional D3 branes on the orbifolds C^2/Z_2 and C^3/(Z_2 x Z_2). In particular we show that the logarithmic divergences in the closed string channel, interpreted as due to twisted massless tadpoles, are mapped, under open/closed string duality, in the logarithmic ones in the open string channel, due to the massless states circulating in the annulus diagram and corresponding to the one-loop divergences that one finds in the gauge theory living in the world volume of the brane. This result provides a quantitative evidence of why the chiral and scale anomalies of the supersymmetric and non conformal gauge theories supported by the world volume of the branes can be inferred from supergravity calculations.Comment: LaTeX, 8 pages. Contribution to the proceedings of the workshop of the RTN Network "The quantum structure of space-time and the geometric nature of fundamental interactions", Copenhagen, September 200

analytical stiffness matrix for curved metal wires

Abstract The paper presents an analytic stiffness matrix for curved thin metal wires, derived by the application of the second Castigliano's Theorem. The matrix accounts both bending and axial stiffness contributions in plane. The beam geometry is described by a cubic polynomial function of the curvature radius with a monotonical attitude angle as the independent variable. The solution proposed if fully analytical although a consistent number of adding factors appear. Some test cases are discussed and compared with Finite Element solutions, formed by a plentiful assembly of straight beams

N=1 Matter from Fractional Branes

We study a bound state of fractional D3-branes localized inside the world-volume of fractional D7-branes on the orbifold C^3/Z_2 x Z_2. We determine the open string spectrum that leads to N=1 U(N1)xU(N2)xU(N3)xU(N4) gauge theory with matter having the number of D7-branes as a flavor index. We derive the linearized boundary action of the D7-brane on this orbifold using the boundary state formalism and we discuss the tadpole cancellation. After computing the asymptotic expression of the supergravity solution the anomalies of the gauge theory are reproduced.Comment: LaTeX 20 pages, 1 figure, small changes and references adde