1,720,978 research outputs found
Universal distributions from non-Hermitian perturbation of zero modes.
No full textKieburg M, Mielke A, Rud M, Splittorff K. Universal distributions from non-Hermitian perturbation of zero modes. Physical review. E. 2020;101(3): 32117.Hermitian operators with exact zero modes subject to non-Hermitian perturbations are considered. Specific focus is on the distribution of the former zero eigenvalues of the Hermitian operators. The broadening of these zero modes is found to follow an elliptic Gaussian random matrix ensemble of fixed size, where the symmetry class of the perturbation determines the behavior of the modes. This distribution follows from a central limit theorem of matrices and is shown to be robust to deformations
Baryon Number Dirac Spectrum in QCD
No full textIpsen J, Splittorff K. Baryon Number Dirac Spectrum in QCD. Phys. Rev. D. 2012;86(1): 14508.The relation between the baryon number in QCD at nonzero chemical potentialand the spectral density of the baryon number Dirac operator, ,is examined. We show that extreme oscillations of the spectral density, causedby the QCD sign problem, are essential for the formation of the average baryonnumber when . We compute the oscillating region of the spectraldensity using chiral perturbation theory. The extreme oscillations have amicroscopic period and are resolved using random matrix theory
Effects of dynamical quarks on the spectrum of the Wilson Dirac operator
No full textAkemann G, Damgaard PH, Splittorff K, Verbaarschot JJM. Effects of dynamical quarks on the spectrum of the Wilson Dirac operator. In: PoS LATTICE. Vol 2010. 2010: 079.Effects of dynamical quarks on the microscopic spectrum of the Wilson Diracoperator are analyzed by means of effective field theory. We consider thedistributions of the real modes of the Wilson Dirac operator as well as thespectrum of the Hermitian Wilson Dirac operator, and work out the case of oneflavor in all detail. In contrast to the quenched case, the theory has a mildsign problem that manifests itself by giving a spectral density that is notpositive definite as the spectral gap closes
Universal broadening of zero modes: A general framework and identification
Full text linkKieburg M, Mielke A, Splittorff K. Universal broadening of zero modes: A general framework and identification. PHYSICAL REVIEW E. 2019;99(5): 52112.We consider the smallest eigenvalues of perturbed Hermitian operators with zero modes, either topological or system specific. To leading order for small generic perturbation we show that the corresponding eigenvalues broaden to a Gaussian random matrix ensemble of size nu x nu, where nu is the number of zero modes. This observation unifies and extends a number of results within chiral random matrix theory and effective field theory and clarifies under which conditions they apply. The scaling of the former zero modes with the volume differs from the eigenvalues in the bulk, which we propose as an indicator to identify them in experiments. These results hold for all 10 symmetric spaces in the Altland-Zirnbauer classification and build on two facts. First, the broadened zero modes decouple from the bulk eigenvalues and, second, the mixing from eigenstates of the perturbation form a central limit theorem argument for matrices
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
Wilson Fermions, Random Matrix Theory and the Aoki Phase
No full textAkemann G, Damgaard PH, Splittorff K, Verbaarschot JJM. Wilson Fermions, Random Matrix Theory and the Aoki Phase. In: PoS (Lattice 2010). Vol 92. 2010.The QCD partition function for the Wilson Dirac operator, , at nonzerolattice spacing can be expressed in terms of a chiral Lagrangian as asystematic expansion in the quark mass, the momentum and . Starting fromthis chiral Lagrangian we obtain an analytical expression for the spectraldensity of in the microscopic domain. It is shown that the-Hermiticity of the Dirac operator necessarily leads to a coefficientof the term that is consistent with the existence of an Aoki phase. Thetransition to the Aoki phase is explained, and the interplay of the index of and nonzero is discussed. We formulate a random matrix theory for theWilson Dirac operator with index (which, in the continuum limit, becomesequal to the topological charge of gauge field configurations). It is shown byan explicit calculation that this random matrix theory reproduces the-dependence of the chiral Lagrangian in the microscopic domain, and thatthe sign of the -term is directly related to the -Hermiticity of
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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