1,700 research outputs found
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 ‘being at home’ 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 ‘being at home’ 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)
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
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