27 research outputs found
Conformal Field Theory Correlators from Classical Field Theory on Anti-de Sitter Space II. Vector and Spinor Fields
We use the AdS/CFT correspondence to calculate CFT correlation functions of
vector and spinor fields. The connection between the AdS and boundary fields is
properly treated via a Dirichlet boundary value problem.Comment: 14 pages, LaTeX2e with amsmath,amsfonts packages; v2:interactions
section corrected, reference adde
8-Vertex Correlation Functions and Twist Covariance of q-KZ Equation
We study the vertex operators associated with standard quantum
groups. The element is a "Casimir operator" for quantized
Kac-Moody algebras and the quantum Knizhnik-Zamolodchikov (q-KZ) equation is
interpreted as the statement . We study the covariance of
the q-KZ equation under twisting, first within the category of Hopf algebras,
and then in the wider context of quasi Hopf algebras. We obtain the
intertwining operators associated with the elliptic R-matrix and calculate the
two-point correlation function for the eight-vertex model.Comment: 31 pages. Plain Te
Reissner-Nordstrom and charged gas spheres
The main point of this paper is a suggestion about the proper treatment of
the photon gas in a theory of stellar structure and other plasmas. This problem
arises in the study of polytropic gas spheres, where we have already introduced
some innovations. The main idea, already advanced in the contextof neutral,
homogeneous, polytropic stellar models, is to base the theory firmly on a
variational principle. Another essential novelty is to let mass distribution
extend to infinity, the boundary between bulk and atmosphere being defined by
an abrupt change in the polytropic index, triggered by the density. The logical
next step in this program is to include the effect of radiation, which is a
very significant complication since a full treatment would have to include an
account of ionization, thus fieldsrepresenting electrons, ions, photons,
gravitons and neutral atoms as well. In way of preparation, we consider models
that are charged but homogeneous, involving only gravity, electromagnetism and
a single scalar field that represents both the mass and the electric charge; in
short, anon-neutral plasma. While this work only represents a stage in the
development of a theory of stars, without direct application to physical
systems, it does shed some light on the meaning of the Reissner-Nordstrom
solution of the modified Einstein-Maxwell equations., with an application to a
simple system.Comment: 19 pages, plain te
Ideal Stars and General Relativity
We study a system of differential equations that governs the distribution of
matter in the theory of General Relativity. The new element in this paper is
the use of a dynamical action principle that includes all the degrees of
freedom, matter as well as metric. The matter lagrangian defines a relativistic
version of non-viscous, isentropic hydrodynamics. The matter fields are a
scalar density and a velocity potential; the conventional, four-vector velocity
field is replaced by the gradient of the potential and its scale is fixed by
one of the eulerian equations of motion, an innovation that significantly
affects the imposition of boundary conditions. If the density is integrable at
infinity, then the metric approaches the Schwarzschild metric at large
distances. There are stars without boundary and with finite total mass; the
metric shows rapid variation in the neighbourhood of the Schwarzschild radius
and there is a very small core where a singularity indicates that the gas laws
break down. For stars with boundary there emerges a new, critical relation
between the radius and the gravitational mass, a consequence of the stronger
boundary conditions. Tentative applications are suggested, to certain Red
Giants, and to neutron stars, but the investigation reported here was limited
to polytropic equations of state. Comparison with the results of Oppenheimer
and Volkoff on neutron cores shows a close agreement of numerical results.
However, in the model the boundary of the star is fixed uniquely by the
required matching of the interior metric to the external Schwarzschild metric,
which is not the case in the traditional approach.Comment: 26 pages, 7 figure
Quantization on Curves
Deformation quantization on varieties with singularities offers perspectives
that are not found on manifolds. Essential deformations are classified by the
Harrison component of Hochschild cohomology, that vanishes on smooth manifolds
and reflects information about singularities. The Harrison 2-cochains are
symmetric and are interpreted in terms of abelian -products. This paper
begins a study of abelian quantization on plane curves over \Crm, being
algebraic varieties of the form R2/I where I is a polynomial in two variables;
that is, abelian deformations of the coordinate algebra C[x,y]/(I).
To understand the connection between the singularities of a variety and
cohomology we determine the algebraic Hochschild (co-)homology and its
Barr-Gerstenhaber-Schack decomposition. Homology is the same for all plane
curves C[x,y]/(I), but the cohomology depends on the local algebra of the
singularity of I at the origin.Comment: 21 pages, LaTex format. To appear in Letters Mathematical Physic
Basic Hypergeometric Functions and Covariant Spaces for Even Dimensional Representations of U_q[osp(1/2)]
Representations of the quantum superalgebra U_q[osp(1/2)] and their relations
to the basic hypergeometric functions are investigated. We first establish
Clebsch-Gordan decomposition for the superalgebra U_q[osp(1/2)] in which the
representations having no classical counterparts are incorporated. Formulae for
these Clebsch-Gordan coefficients are derived, and it is observed that they may
be expressed in terms of the -Hahn polynomials. We next investigate
representations of the quantum supergroup OSp_q(1/2) which are not well-defined
in the classical limit. Employing the universal T-matrix, the representation
matrices are obtained explicitly, and found to be related to the little
Q-Jacobi polynomials. Characteristically, the relation Q = -q is satisfied in
all cases. Using the Clebsch-Gordan coefficients derived here, we construct new
noncommutative spaces that are covariant under the coaction of the even
dimensional representations of the quantum supergroup OSp_q(1/2).Comment: 16 pages, no figure
Knowledge mobilization in the context of health technology assessment: an exploratory case study
<p>Abstract</p> <p>Background</p> <p>Finding measures to enhance the dissemination and implementation of their recommendations has become part of most health technology assessment (HTA) bodies' preoccupations. The Quebec government HTA organization in Canada observed that some of its projects relied on innovative practices in knowledge production and dissemination. A research was commissioned in order to identify what characterized these practices and to establish whether they could be systematized.</p> <p>Methods</p> <p>An exploratory case study was conducted during summer and fall 2010 in the HTA agency in order to determine what made the specificity of its context, and to conceptualize an approach to knowledge production and dissemination that was adapted to the mandate and nature of this form of HTA organization. Six projects were selected. For each, the HTA report and complementary documents were analyzed, and semi-structured interviews were carried out. A narrative literature review of the most recent literature reviews of the principal knowledge into practice frameworks (2005-2010) and of articles describing such frameworks (2000-2010) was undertaken.</p> <p>Results and discussion</p> <p>Our observations highlighted an inherent difficulty as regards applying the dominant knowledge translation models to HTA and clinical guidance practices. For the latter, the whole process starts with an evaluation question asked in a problematic situation for which an actionable answer is expected. The objective is to produce the evidence necessary to respond to the decision-maker's request. The practices we have analyzed revealed an approach to knowledge production and dissemination, which was multidimensional, organic, multidirectional, dynamic, and dependent on interactions with stakeholders. Thus, HTA could be considered as a knowledge mobilization process per se.</p> <p>Conclusions</p> <p>HTA's purpose is to solve a problem by mobilizing the types of evidence required and the concerned actors, in order to support political, organizational or clinical decision-making. HTA relies on the mediation between contextual, colloquial and scientific evidence, as well as on interactions with stakeholders for recommendation making. Defining HTA as a knowledge mobilization process might contribute to consider the different orders of knowledge, the social, political and ethical dimensions, and the interactions with stakeholders, among the essential components required to respond to the preoccupations, needs and contexts of all actors concerned with the evaluation question's issues.</p