873 research outputs found
Conformal Field Theories, Graphs and Quantum Algebras
This article reviews some recent progress in our understanding of the
structure of Rational Conformal Field Theories, based on ideas that originate
for a large part in the work of A. Ocneanu. The consistency conditions that
generalize modular invariance for a given RCFT in the presence of various types
of boundary conditions --open, twisted-- are encoded in a system of integer
multiplicities that form matrix representations of fusion-like algebras. These
multiplicities are also the combinatorial data that enable one to construct an
abstract ``quantum'' algebra, whose - and -symbols contain essential
information on the Operator Product Algebra of the RCFT and are part of a cell
system, subject to pentagonal identities. It looks quite plausible that the
classification of a wide class of RCFT amounts to a classification of ``Weak
- Hopf algebras''.Comment: 23 pages, 12 figures, LateX. To appear in MATHPHYS ODYSSEY 2001
--Integrable Models and Beyond, ed. M. Kashiwara and T. Miwa, Progress in
Math., Birkhauser. References and comments adde
On the crossing relation in the presence of defects
The OPE of local operators in the presence of defect lines is considered both
in the rational CFT and the Virasoro (Liouville) theory. The duality
transformation of the 4-point function with inserted defect operators is
explicitly computed. The two channels of the correlator reproduce the
expectation values of the Wilson and 't Hooft operators, recently discussed in
Liouville theory in relation to the AGT conjecture.Comment: TEX file with harvmac; v3: JHEP versio
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Acts of terrorism and mass violence targeting schools : Analysis and implications for preparedness in the USA
To enhance the preparedness of US schools to acts of terrorism and mass violence, the landscape of threats against schools must first be understood. This includes exploring the global trends of acts of terrorism against schools, as well as looking specifically at the history of terrorism and acts of mass violence against schools domestically. This paper conducts a review of two databases in order to look at the trends in acts of terrorism and mass violence carried out against schools, and provides recommendations for domestic school preparedness based on this information
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Schools and Terrorism: Global Trends, Impacts, and Lessons for Resilience
This study characterizes trends in the frequency and characteristics of terrorist attacks in child-serving educational institutions around the world, examining the specific vulnerabilies of children and schools with regard to terrorist violence, as well as the various impacts that violence has on children, communities, and societies. Following the analysis of available data on terrorist attacks against educational institutions, vulnerabilities, and impacts, the study concludes with a discussion of what still needs to be understood in the intersection of child vulnerability and terrorism, and provides recommendations for improving resilience to terrorist attacks against child-serving educational institutions.
One would like to think that certain truths or values would be universally understood as rules of engagement, formally declared or otherwise. The sanctity of children's well-being should be unquestioned, regardless of the issues at stake in the larger conflict. Sadly, history shows that this understanding is neither universally shared nor uniformly valued.
âIrwin Redlener, Americans at Risk, 2007
Since the violent attack on School Number One in Beslan, Russia in 2004, the perceived threat of massive terror attacks targeting schoolchildren has loomed in the public consciousness. In recent years, attacks against educational institutions worldwide have increasingly been reported and documented. The kidnapping of 276 schoolgirls by Boko Haram in Nigeria and the massacre of at least 150 students and staff in a Peshawar school by the Pakistani Taliban in 2014 are still fresh in the minds of the public. These attacks serve as reminders of the vulnerability that children in schools face, being âsoft targetsâ whose symbolic value has the capacity of invoking mayhem at the largest possible scale. They also demonstrate the urgency with which this emerging trend in violence must be systemically recorded, analyzed, and mitigated.
The following article will discuss the vulnerability of children with regard to terrorist violence, exploring the literature on what makes children and educational institutions particularly desirable targets. Trends in the frequency and characteristics of terrorist attacks against child-serving educational institutions around the world will be examined, paying particular attention to potential school level and gendered disparities. Finally, a critical analysis on what can be learned from the available data and what still needs to be researched in the nexus of child vulnerability and terrorism will be provided
Climate Change and Health on the U.S. Gulf Coast: Public Health Adaptation is Needed to Address Future Risks
The impacts of climate change on human health have been documented globally and in the United States. Numerous studies project greater morbidity and mortality as a result of extreme weather events and other climate-sensitive hazards. Public health impacts on the U.S. Gulf Coast may be severe as the region is expected to experience increases in extreme temperatures, sea level rise, and possibly fewer but more intense hurricanes. Through myriad pathways, climate change is likely to make the Gulf Coast less hospitable and more dangerous for its residents, and may prompt substantial migration from and into the region. Public health impacts may be further exacerbated by the concentration of people and infrastructure, as well as the regionâs coastal geography. Vulnerable populations, including the very young, elderly, and socioeconomically disadvantaged may face particularly high threats to their health and well-being. This paper provides an overview of potential public health impacts of climate variability and change on the Gulf Coast, with a focus on the regionâs unique vulnerabilities, and outlines recommendations for improving the regionâs ability to minimize the impacts of climate-sensitive hazards. Public health adaptation aimed at improving individual, public health system, and infrastructure resilience is urgently needed to meet the challenges climate change may pose to the Gulf Coast in the coming decades
The Virtue of Defects in 4D Gauge Theories and 2D CFTs
We advance a correspondence between the topological defect operators in
Liouville and Toda conformal field theories - which we construct - and loop
operators and domain wall operators in four dimensional N=2 supersymmetric
gauge theories on S^4. Our computation of the correlation functions in
Liouville/Toda theory in the presence of topological defect operators, which
are supported on curves on the Riemann surface, yields the exact answer for the
partition function of four dimensional gauge theories in the presence of
various walls and loop operators; results which we can quantitatively
substantiate with an independent gauge theory analysis. As an interesting
outcome of this work for two dimensional conformal field theories, we prove
that topological defect operators and the Verlinde loop operators are different
descriptions of the same operators.Comment: 59 pages, latex; v2 corrections to some formula
't Hooft Operators in Gauge Theory from Toda CFT
We construct loop operators in two dimensional Toda CFT and calculate with
them the exact expectation value of certain supersymmetric 't Hooft and dyonic
loop operators in four dimensional \Ncal=2 gauge theories with SU(N) gauge
group. Explicit formulae for 't Hooft and dyonic operators in \Ncal=2^* and
\Ncal=2 conformal SQCD with SU(N) gauge group are presented. We also briefly
speculate on the Toda CFT realization of arbitrary loop operators in these
gauge theories in terms of topological web operators in Toda CFT.Comment: 49 pages, LaTeX. Typos fixed, references adde
From conformal embeddings to quantum symmetries: an exceptional SU(4) example
We briefly discuss several algebraic tools that are used to describe the
quantum symmetries of Boundary Conformal Field Theories on a torus. The
starting point is a fusion category, together with an action on another
category described by a quantum graph. For known examples, the corresponding
modular invariant partition function, which is sometimes associated with a
conformal embedding, provides enough information to recover the whole
structure. We illustrate these notions with the example of the conformal
embedding of SU(4) at level 4 into Spin(15) at level 1, leading to the
exceptional quantum graph E4(SU(4)).Comment: 22 pages, 3 color figures. Version 2: We changed the color of figures
(ps files) in such a way that they are still understood when converted to
gray levels. Version 3: Several references have been adde
The charges of a twisted brane
The charges of the twisted D-branes of certain WZW models are determined. The
twisted D-branes are labelled by twisted representations of the affine algebra,
and their charge is simply the ground state multiplicity of the twisted
representation. It is shown that the resulting charge group is isomorphic to
the charge group of the untwisted branes, as had been anticipated from a
K-theory calculation. Our arguments rely on a number of non-trivial Lie
theoretic identities.Comment: 27 pages, 1 figure, harvmac (b
Graphs and Reflection Groups
It is shown that graphs that generalize the ADE Dynkin diagrams and have
appeared in various contexts of two-dimensional field theory may be regarded in
a natural way as encoding the geometry of a root system. After recalling what
are the conditions satisfied by these graphs, we define a bilinear form on a
root system in terms of the adjacency matrices of these graphs and undertake
the study of the group generated by the reflections in the hyperplanes
orthogonal to these roots. Some ``non integrally laced " graphs are shown to be
associated with subgroups of these reflection groups. The empirical relevance
of these graphs in the classification of conformal field theories or in the
construction of integrable lattice models is recalled, and the connections with
recent developments in the context of supersymmetric theories and
topological field theories are discussed.Comment: 42 pages TEX file, harvmac and epsf macros, AMS fonts optional,
uuencoded, 8 figures include
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