1,721,047 research outputs found
Hypercubic Effects in semileptonic decays on the lattice
No full textWe present a lattice determination of the vector and scalar form factors of the semileptonic D -> pi l nu decays, which are relevant for the extraction of the CKM matrix element from experimental data. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with N_f = 2 + 1 + 1 flavors of dynamical
quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Quark momenta are injected on the lattice using non-periodic boundary conditions. The matrix elements of both vector and
scalar currents are determined for a plenty of kinematical conditions in which parent and child mesons are either moving or at rest. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data and included in the
decomposition of the current matrix elements in terms of additional form factors. Our preliminary estimate for the vector form factor at zero 4-momentum transfer is f_+(D -> pi)(0) = 0.631(40), which can be compared with the latest FLAG average f_+(D -> pi)(0) = 0.666 (29) available only at N_f = 2 + 1
Hypercubic effects in semileptonic decays of heavy mesons, toward B -> pi l nu with Nf=2+1+1 Twisted fermions
No full textWe present a preliminary study toward a lattice determination of the vector and scalar form factors of the B -> pi l nu semileptonic decays. We compute the form factors relative to the transition between heavy-light pseudoscalar mesons, with masses above the physical D-mass, and the pion. We simulate heavy-quark masses in the range mc^phys < mh < 2 mc^phys. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data, and included in the decomposition of the current matrix elements in terms of additional form factors. We discuss the size of this breaking as the parent-meson mass increases. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2+1+1 flavors of dynamical quarks at three different values of the lattice spacing and with pion masses as small as 210 MeV
K →π semileptonic form factors with Nf=2+1+1 twisted mass fermions
Full text linkWe present a lattice QCD determination of the vector and scalar form factors of the semileptonic K→ decay which are relevant for the extraction of the Cabibbo-Kobayashi-Maskawa matrix element |Vus| from experimental data. Our results are based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 dynamical fermions, which include in the sea, besides two light mass degenerate quarks, also the strange and the charm quarks. We use data simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Our final result for the vector form factor at zero momentum transfer is f+(0)=0.9709(46), where the uncertainty is both statistical and systematic combined in quadrature. Using the latest experimental value of f+(0)|Vus| from K 3 decays, we obtain |Vus|=0.2230(11), which allows us to test the unitarity constraint of the Standard Model below the permille level once the determination of |Vud| from superallowed nuclear β decays is adopted. A slight tension with unitarity at the level of ∼2 standard deviations is observed. Moreover, we present our results for the semileptonic scalar f0(q2) and vector f+(q2) form factors in the whole range of values of the squared four-momentum transfer q2 measured in K 3 decays, obtaining a very good agreement with the momentum dependence of the experimental data. We provide a set of synthetic data points representing our results for the vector and scalar form factors at the physical point for several selected values of q2
Electromagnetic corrections to leptonic decay rates of charged pseudoscalar mesons: finite-volume effects
No full textIn Carrasco et al. we have recently proposed a method to calculate O(e^2) electromagnetic corrections to leptonic decay widths of pseudoscalar mesons. The method is based on the observation that the infrared divergent contributions (that appear at intermediate stages of the calculation and that cancel in physical quantities thanks to the Bloch-Nordsieck mechanism) are
universal, i.e. depend on the charge and the mass of the meson but not on its internal structure. In this talk we perform a detailed analysis of the finite-volume effects associated with our method. In particular we show that also the leading 1/L finite-volume effects are universal and perform an analytical calculation of the finite-volume leptonic decay rate for a
point-like meson
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
Tensor form factor for the <i>D</i> → <i>π(K)</i> transitions with Twisted Mass fermions.
Full text linkWe present a preliminary lattice calculation of the D → π and D → K tensor form factors fT (q2) as a function of the squared 4-momentum transfer q2. ETMC recently computed the vector and scalar form factors f+(q2) and f0(q2) describing D → π(K)lv semileptonic decays analyzing the vector current and the scalar density. The study of the weak tensor current, which is directly related to the tensor form factor, completes the set of hadronic matrix element regulating the transition between these two pseudoscalar mesons within and beyond the Standard Model where a non-zero tensor coupling is possible. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 flavors of dynamical quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV and with the valence heavy quark in the mass range from ≃ 0.7 mc to ≃ 1.2mc. The matrix element of the tensor current are determined for a plethora of kinematical conditions in which parent and child mesons are either moving or at rest. As for the vector and scalar form factors, Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data. We will present preliminary results on the removal of such hypercubic lattice effects.</jats:p
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