1,720,980 research outputs found
Quark forces from hadronic spectroscopy
Full text linkWe consider the implications of the most general two-body quark-quark interaction Hamiltonian for the spin-flavor structure of the negative parity L=1 excited baryons. Assuming the most general two-body quark interaction Hamiltonian, we derive two correlations among the masses and mixing angles of these states, which constrain the mixing angles, and can be used to test for the presence of three-body quark interactions. We find that the pure gluon-exchange model is disfavored by data, independently of any assumptions about hadronic wave functions. © 2009 The American Physical Society.Fil: Pirjol, Dan. Horia Hulubei National Institute Of Physics And Nuclear Engineering;Fil: Schat, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Positive parity pentaquark towers in large N(c) QCD.
Full text linkWe construct the complete set of positive parity pentaquarks, which correspond in the quark model to sq Nc 1 states with one unit of orbital angular momentum L 1. In the large Nc limit they fall into the K 1=2 and K 3=2 irreps (towers) of the contracted SU4 c symmetry. We derive predictions for the mass spectrum and the axial couplings of these states at leading order in 1=Nc. The strong decay width of
the lowest-lying positive parity exotic state is of order O1=Nc , such that this state is narrow in the large Nc limit. Replacing the antiquark with a heavy antiquark Qq Nc 1, the two towers become degenerate, split only by O1=mQ hyperfine interactions. We obtain predictions for the strong decay widths of heavy pentaquarks to ordinary baryons and heavy H Q mesons at leading order in 1=Nc and 1=mQ.Fil: Pirjol. Dan. Massachusetts Institute of Technology; Estados UnidosFil: Schat, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Permutation group SN and large Nc excited baryons
Full text linkWe study the excited baryon states for an arbitrary number of colors Nc from the perspective of the permutation group SN of N objects. Classifying the transformation properties of states and quark-quark interaction operators under SN allows a general analysis of the spin-flavor structure of the mass operator of these states, in terms of a few unknown constants parametrizing the unknown spatial structure. We explain how to perform the matching calculation of a general two-body quark-quark interaction onto the operators of the 1/Nc expansion. The inclusion of core and excited quark operators is shown to be necessary. Considering the case of the negative parity L=1 states transforming in the MS of SN, we discuss the matching of the one-gluon and the Goldstone-boson exchange interactions. © 2008 The American Physical Society.Fil: Pirjol, Dan. Horia Hulubei National Institute Of Physics And Nuclear Engineering; RumaniaFil: Schat, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Murcia; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Negative parity pentaquarks in large Nc QCD and quark model
Full text linkRecently, the 1/Nc expansion has been applied to the study of exotic baryons containing both quarks and antiquarks. We extend this approach to exotic states with mixed-symmetric spin-flavor symmetry, which correspond in the quark model to negative parity pentaquarks, and discuss the large N c predictions for their mass spectrum. The heavy exotics Q̄q4 transform as 3, 6, 15 and 15′ under SU(3), while the light states q̄q4 include the exotic multiplets 10, 27, 35. We give mass relations among these multiplets in the 1/Nc expansion. In the quark model, the mass splittings between these states are given by color-spin interactions. Using the observation of an anticharmed exotic by the H1 Collaboration, we give predictions for the masses of other expected heavy pentaquarks. © 2005 The American Physical Society.Fil: Pirjol, Dan. Mit Center For Theoretical Physics; Estados UnidosFil: Schat, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Isgur-Karl model revisited
Full text linkWe show how to match the Isgur-Karl model to the spin-flavor quark operator expansion used in the 1/Nc studies of the nonstrange negative parity L=1 excited baryons. Using the transformation properties of states and interactions under the permutation group S3 we are able to express the operator coefficients as overlap integrals, without making any assumption on the spatial dependence of the quark wave functions. The general mass operator leads to parameter free mass relations and constraints on the mixing angles that are valid beyond the usual harmonic oscillator approximation. The Isgur-Karl model with harmonic oscillator wave functions provides a simple counterexample that demonstrates explicitly that the alternative operator basis for the 1/Nc expansion for excited baryons recently proposed by Matagne and Stancu is incomplete. © 2009 The American Physical Society.Fil: Galeta, Leonardo Javier. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Pirjol, Dan. Horia Hulubei National Institute Of Physics And Nuclear Engineering; RumaniaFil: Schat, Carlos Luis. Universidad de Buenos Aires; Argentina. Ohio University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
1/Nc expansion and the spin-flavor structure of the quark interaction in the constituent quark model
Full text linkWe study the hierarchy of the coefficients in the 1/Nc expansion for the negative parity L=1 excited baryons from the perspective of the constituent quark model. This is related to the problem of determining the spin-flavor structure of the quark interaction. The most general two-body scalar interaction between quarks contains the spin-flavor structures t1at2a,s →1•s→2 and s→1•s →2t1at2a. We show that in the limit of a zero range interaction all these structures are matched onto the same hadronic mass operator Sc2, which gives a possible explanation for the dominance of this operator in the 1/N c expansion for the L=1 states and implies that in this limit it is impossible to distinguish between these different spin-flavor structures. Modeling a finite range interaction through the exchange of a vector and pseudoscalar meson, we propose a test for the spin-flavor dependence of the quark forces. For the scalar part of the quark interaction, we find that both pion exchange and gluon exchange are compatible with the data. © 2010 The American Physical Society.Fil: Pirjol, Dan. Horia Hulubei National Institute Of Physics And Nuclear Engineering; RumaniaFil: Schat, Carlos Luis. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física. Grupo de Física de Altas Energías y Partículas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
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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