1,721,008 research outputs found
Anomalies in field theories with extra dimensions
Full text linkWe give an overview of the issue of anomalies in field theories with extra dimensions. We start by reviewing in a pedagogical way the computation of the standard perturbative gauge and gravitational anomalies on non-compact spaces, using Fujikawa's approach and functional integral methods, and discuss the available mechanisms for their cancellation. We then generalize these analyses to the case of orbifold field theories with compact internal dimensions, emphasizing the new aspects related to the presence of orbifold singularities and discrete Wilson lines, and the new cancellation mechanisms that are becoming available. We conclude with a very brief discussion on global and parity anomalies.We give an overview of the issue of anomalies in field theories with extra dimensions. We start by reviewing in a pedagogical way the computation of the standard perturbative gauge and gravitational anomalies on non-compact spaces, using Fujikawa's approach and functional integral methods, and discuss the available mechanisms for their cancellation. We then generalize these analyses to the case of orbifold field theories with compact internal dimensions, emphasizing the new aspects related to the presence of orbifold singularities and discrete Wilson lines, and the new cancellation mechanisms that are becoming available. We conclude with a very brief discussion on global and parity anomalies
Electric and magnetic interaction of dyonic D-branes and odd spin structure
No full textWe present a general description of electromagnetic RR interactions between pairs of magnetically dual D-branes, focusing on the interaction of a magnetically charged brane with an electrically charged one. In the boundary state formalism, it turns out that while the electric-electric and/or magnetic-magnetic interaction corresponds to the usual RR even spin structure, the magnetic-electric interaction is described by the RR odd spin structure. As representative of the generic case of a dual pair of p and 6-p-branes, we discuss in detail the case of the self-dual 3-brane wrapped on a T-6/Z(3), which looks like an extremal dyonic black hole in four dimensions
D3-branes dynamics and black holes
No full textWe adress tno aspects of D-branes physics. The first regards the interaction between two electromagnetic dual D-branes in 10 dimensions. In particular, we give a meaning to both even and odd spin structure contributions, the latter being non vanishing and encoding the Lorentz-like contribution. The second aspect regards the D-brane/black holes correspondence. We show how the 4 dimensional configuration corresponding to a single D3-brane wrapped on T-6/Z(3) represents a regular solution of d=4N=2 supergravity
Black holes as D-branes on Calabi-Yau threefolds
No full textWe show how an extremal Reissner-Nordstrom black hole can be obtained by wrapping a dyonic D3-brane on a Calabi-Yau manifold. In the orbifold limit T-6/Z(3), We explicitly show the correspondence between the solution of the supergravity equations of motion and the D-brane boundary state description of such a black hole
Anomalous couplings for D-branes and O-planes
Full text linkWe study anomalous Wess-Zumino couplings of D-branes and O-planes in a general background and derive them from a direct string computation by factorizing in the RR channel various one-loop amplitudes, In particular, we find that Op-planes present gravitational anomalous couplings involving the Hirzebruch polynomial (L) over cap, similarly to the roof genus (A) over cap encoding Dp-brane anomalous couplings, We determine, in each case, the precise dependence of these couplings on the curvature of the tangent and normal bundles. (C) 1999 Elsevier Science B.V. All rights reserved.GR-S
Open string models with Scherk-Schwarz SUSY breaking and localized anomalies
No full textWe study examples of chiral four-dimensional IIB orientifolds with Scherk-Schwarz supersymmetry breaking, based on freely acting orbifolds. We construct a new Z_3 x Z_3' model, containing only D9-branes, and rederive from a more geometric perspective the known Z_6' x Z_2' model, containing D9, D5 and \bar D 5 branes. The cancellation of anomalies in these models is then studied locally in the internal space. These are found to cancel through an interesting generalization of the Green-Schwarz mechanism involving twisted Ramond-Ramond axions and four-forms. The effect of the latter amounts to local counterterms from a low-energy effective field theory point of view.We study examples of chiral four-dimensional IIB orientifolds with Scherk–Schwarz supersymmetry breaking, based on freely acting orbifolds. We construct a new Z 3 × Z ′ 3 model, containing only D9-branes, and rederive from a more geometric perspective the known Z ′ 6 × Z ′ 2 model, containing D9, D5 and D 5 branes. The cancellation of anomalies in these models is then studied locally in the internal space. These are found to cancel through an interesting generalization of the Green–Schwarz mechanism involving twisted Ramond–Ramond axions and 4-forms. The effect of the latter amounts to local counterterms from a low-energy effective field theory point of view. We also point out that the number of spontaneously broken U (1) gauge fields is in general greater than what expected from a four-dimensional analysis of anomalies.We study examples of chiral four-dimensional IIB orientifolds with Scherk--Schwarz supersymmetry breaking, based on freely acting orbifolds. We construct a new Z3xZ3' model, containing only D9-branes, and rederive from a more geometric perspective the known Z6'xZ2' model, containing D9, D5 and \bar D 5 branes. The cancellation of anomalies in these models is then studied locally in the internal space. These are found to cancel through an interesting generalization of the Green--Schwarz mechanism involving twisted Ramond--Ramond axions and 4-forms. The effect of the latter amounts to local counterterms from a low-energy effective field theory point of view. We also point out that the number of spontaneously broken U(1) gauge fields is in general greater than what expected from a four-dimensional analysis of anomalies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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