Quantization of Wilson loops in Wess-Zumino-Witten models

We describe a non-perturbative quantization of classical Wilson loops in the WZW model. The quantized Wilson loop is an operator acting on the Hilbert space of closed strings and commuting either with the full Kac-Moody chiral algebra or with one of its subalgebras. We prove that under open/closed string duality, it is dual to a boundary perturbation of the open string theory. As an application, we show that such operators are useful tools for identifying fixed points of the boundary renormalization group flow.Comment: 24 pages. Version published in JHE

Moyal Representation of the String Field Star Product in the Presence of a B-background

In this paper we show that in the presence of an anti-symmetric tensor $B$-background, Witten's star algebra for open string fields persists to possess the structure of a direct product of commuting Moyal pairs. The interplay between the noncommutativity due to three-string overlap and that due to the $B$-background is our main concern. In each pair of noncommutative directions parallel to the $B$-background, the Moyal pairs mix string modes in the two directions and are labeled, in addition to a continuous parameter, by {\it two} discrete values as well. However, the Moyal parameters are $B$-dependent only for discrete pairs. We have also demonstrated the large-$B$ contraction of the star algebra, with one of the discrete Moyal pairs dropping out while the other giving rise to the center-of-mass noncommutative function algebra.Comment: minor notation chang

Witten's Vertex Made Simple

The infinite matrices in Witten's vertex are easy to diagonalize. It just requires some SL(2,R) lore plus a Watson-Sommerfeld transformation. We calculate the eigenvalues of all Neumann matrices for all scale dimensions s, both for matter and ghosts, including fractional s which we use to regulate the difficult s=0 limit. We find that s=1 eigenfunctions just acquire a p term, and x gets replaced by the midpoint position.Comment: 24 pages, 2 figures, RevTeX style, typos correcte

An oncogenic role for sphingosine kinase 2

While both human sphingosine kinases (SK1 and SK2) catalyze the generation of the pleiotropic signaling lipid sphingosine 1-phosphate, these enzymes appear to be functionally distinct. SK1 has well described roles in promoting cell survival, proliferation and neoplastic transformation. The roles of SK2, and its contribution to cancer, however, are much less clear. Some studies have suggested an antiproliferative/ pro-apoptotic function for SK2, while others indicate it has a prosurvival role and its inhibition can have anti-cancer effects. Our analysis of gene expression data revealed that SK2 is upregulated in many human cancers, but only to a small extent (up to 2.5-fold over normal tissue). Based on these findings, we examined the effect of different levels of cellular SK2 and showed that high-level overexpression reduced cell proliferation and survival, and increased cellular ceramide levels. In contrast, however, low-level SK2 overexpression promoted cell survival and proliferation, and induced neoplastic transformation in vivo. These findings coincided with decreased nuclear localization and increased plasma membrane localization of SK2, as well as increases in extracellular S1P formation. Hence, we have shown for the first time that SK2 can have a direct role in promoting oncogenesis, supporting the use of SK2-specific inhibitors as anti-cancer agents.Heidi A. Neubauer, Duyen H. Pham, Julia R. Zebol, Paul A.B. Moretti, Amanda L. Peterson, Tamara M. Leclercq, Huasheng Chan, Jason A. Powell, Melissa R. Pitman, Michael S. Samuel, Claudine S. Bonder, Darren J. Creek, Briony L. Gliddon and Stuart M. Pitso

Noncommutative Self-dual Gravity

Starting from a self-dual formulation of gravity, we obtain a noncommutative theory of pure Einstein theory in four dimensions. In order to do that, we use Seiberg-Witten map. It is shown that the noncommutative torsion constraint is solved by the vanishing of commutative torsion. Finally, the noncommutative corrections to the action are computed up to second order.Comment: 15+1 pages, LaTeX, no figure

Abelian and nonabelian vector field effective actions from string field theory

The leading terms in the tree-level effective action for the massless fields of the bosonic open string are calculated by integrating out all massive fields in Witten's cubic string field theory. In both the abelian and nonabelian theories, field redefinitions make it possible to express the effective action in terms of the conventional field strength. The resulting actions reproduce the leading terms in the abelian and nonabelian Born-Infeld theories, and include (covariant) derivative corrections.Comment: 49 pages, 1 eps figur

String Field Theory Vertices for Fermions of Integral Weight

We construct Witten-type string field theory vertices for a fermionic first order system with conformal weights (0,1) in the operator formulation using delta-function overlap conditions as well as the Neumann function method. The identity, the reflector and the interaction vertex are treated in detail paying attention to the zero mode conditions and the U(1) charge anomaly. The Neumann coefficients for the interaction vertex are shown to be intimately connected with the coefficients for bosons allowing a simple proof that the reparametrization anomaly of the fermionic first order system cancels the contribution of two real bosons. This agrees with their contribution c=-2 to the central charge. The overlap equations for the interaction vertex are shown to hold. Our results have applications in N=2 string field theory, Berkovits' hybrid formalism for superstring field theory, the \eta\xi-system and the twisted bc-system used in bosonic vacuum string field theory.Comment: 1+28 pages, minor improvements, references adde

Kondo flow invariants, twisted K-theory and Ramond-Ramond charges

We take a worldsheet point of view on the relation between Ramond-Ramond charges, invariants of boundary renormalization group flows and K-theory. In compact super Wess-Zumino-Witten models, we show how to associate invariants of the generalized Kondo renormalization group flows to a given supersymmetric boundary state. The procedure involved is reminiscent of the way one can probe the Ramond-Ramond charge carried by a D-brane in conformal field theory, and the set of these invariants is isomorphic to the twisted K-theory of the Lie group. We construct various supersymmetric boundary states, and we compute the charges of the corresponding D-branes, disproving two conjectures on this subject. We find a complete agreement between our algebraic charges and the geometry of the D-branes.Comment: 58 pages. V4 : Problem with the bibliography correcte

Solving Witten's string field theory using the butterfly state

We solve the equation of motion of Witten's cubic open string field theory in a series expansion using the regulated butterfly state. The expansion parameter is given by the regularization parameter of the butterfly state, which can be taken to be arbitrarily small. Unlike the case of level truncation, the equation of motion can be solved for an arbitrary component of the Fock space up to a positive power of the expansion parameter. The energy density of the solution is well-defined and remains finite even in the singular butterfly limit, and it gives approximately 68% of the D25-brane tension for the solution at the leading order. Moreover, it simultaneously solves the equation of motion of vacuum string field theory, providing support for the conjecture at this order. We further improve our ansatz by taking into account next-to-leading terms, and find two numerical solutions which give approximately 88% and 109%, respectively, of the D25-brane tension for the energy density. These values are interestingly close to those by level truncation at level 2 without gauge fixing studied by Rastelli and Zwiebach and by Ellwood and Taylor.Comment: 38 pages, no figures, LaTeX2e; v2: the footnote on hep-th/0302151 changed and moved to the introduction; v3: minor typos corrected, published versio

Antimicrobial Stewardship Implementation in Nigerian Hospitals: Gaps and Challenges

Background: Antimicrobial resistance (AMR) is a major clinical challenge globally. It is mainly a consequence of inappropriate prescribing and use of antibiotics. Antimicrobial stewardship (AMS) ensures that antibiotics are prescribed and used appropriately. This study assessed AMS practice in selected Nigerian hospitals.Methodology: This was a cross sectional survey of 20 Federal, State and Private tertiary hospitals randomly selected from the six geopolitical zones of Nigeria. Using an adapted WHO tool on AMS, data were collected from each hospital as regard the existence of AMS committee, Accountability and Responsibility, AMS actions, Education and Training, Monitoring and Evaluation, Infection Prevention and Control (IPC) practice, facilities to support AMS, and challenges to AMS implementation. Gaps and challenges to the implementation of the AMS among the hospitals were identified.Results: Only 6 (30%) of the 20 hospitals had AMS committees while 2 (10%) had any evidence of leadership commitment to AMS. All the hospitals had laboratory facilities to support culture and sensitivity testing. There were no regular AMS-related education or training, monitoring, evaluation or reporting activities in the hospitals, except in 7 (25%) that had participated in the global point prevalence survey (Global-PPS) of antimicrobial use and resistance being hosted by the University of Antwerp, Belgium. Challenges impeding AMS activities included lack of human and financial resources, prescribers’ opposition, lack of awareness and absence of AMS committees. Most of the gaps and challenges bordered on seeming lack of knowledge and inadequate communication among prescribers and other stakeholders.Conclusion: There is need for intense education and training activities for prescribers and other stakeholders, including but not limited to hospital administrators. Keywords: Survey, Antimicrobial Stewardship, Antimicrobial Resistance; Nigeria   French title: Mise en œuvre de la gestion des antimicrobiens dans les hôpitaux Nigérians: lacunes et défis Contexte: La résistance aux antimicrobiens (RAM) est un défi clinique majeur à l'échelle mondiale. C'estprincipalement une conséquence d'une prescription et d'une utilisation inappropriées d'antibiotiques. La gestion des antimicrobiens (AMS) garantit que les antibiotiques sont prescrits et utilisés de manière appropriée. Cette étude a évalué la pratique de l'AMS dans certains hôpitaux Nigérians. Méthodologie: Il s'agissait d'une enquête transversale de 20 hôpitaux tertiaires fédéraux, d'État et privéssélectionnés au hasard dans les six zones géopolitiques du Nigéria. À l'aide d'un outil OMS adapté sur l'AMS, des données ont été collectées auprès de chaque hôpital en ce qui concerne l'existence d'un comité AMS, la responsabilité et la responsabilité, les actions AMS, l'éducation et la formation, le suivi et l'évaluation, la  pratique de prévention et de contrôle des infections (IPC), les installations pour soutenir l'AMS. et les défis de la mise en œuvre de l'AMS. Les lacunes et les défis liés à la mise en œuvre de l'AMS parmi les hôpitaux ont été identifiés. Résultats: Seuls 6 (30%) des 20 hôpitaux avaient des comités AMS tandis que 2 (10%) avaient des preuves d'engagement du leadership envers l'AMS. Tous les hôpitaux disposaient d'installations de laboratoire pour soutenir la culture et les tests de sensibilité. Il n'y avait pas d'activités régulières d'éducation ou de formation, de suivi, d'évaluation ou de rapportage liées à la MGS dans les hôpitaux, sauf dans 7 (25%) qui avaient participé à l'enquête mondiale sur la prévalence ponctuelle (Global-PPS) de l'utilisation et de la résistance aux  antimicrobiens organisée par l'Université d'Anvers, Belgique. Les défis entravant les activités de l'AMS  comprenaient le manque de ressources humaines et financières, l'opposition des prescripteurs, le manque de sensibilisation et l'absence de comités AMS. La plupart des lacunes et des défis se limitaient à un manque apparent de connaissances et à une communication inadéquate entre les prescripteurs et les autres intervenants.Conclusion: Des activités d'éducation et de formation intensives sont nécessaires pour les prescripteurs et autres intervenants, y compris, mais sans s'y limiter, les administrateurs d'hôpitaux. Mots clés: enquête, gestion des antimicrobiens, résistance aux antimicrobiens; Nigeria   &nbsp