1,720,989 research outputs found
Third order correction to semileptonic decay: fermionic contributions
Full text linkWe present the QCD corrections of order αs3 to the decay rate of b→uℓν¯ℓ, with ℓ=e, μ, originating from diagrams with closed fermion loops and neglecting the mass of the up quark. Our calculation relies on integration-by-parts reduction of Feynman integrals with one propagator raised to a symbolic power in kira and the numerical evaluation of master integrals with amflow. This allows us to obtain results for the fermionic contributions to the total semileptonic rate with an accuracy of more than 30 digits.We present the QCD corrections of order to the decay rate of , with , originating from diagrams with closed fermion loops and neglecting the mass of the up quark. Our calculation relies on integration-by-parts reduction of Feynman integrals with one propagator raised to a symbolic power in Kira and the numerical evaluation of master integrals with AMFlow. This allows us to obtain results for the fermionic contributions to the total semileptonic rate with an accuracy of more than thirty digits
Taming the N3LO corrections to semileptonic b -> u decay
No full textWe review the calculation of the QCD corrections of order α3s to the decay rate of b→ulν, originating from diagrams with closed fermion loops and neglecting the mass of the up quark. Our calculation takes advantage of integration-by-parts reduction of Feynman integrals with one propagator raised to a symbolic power in Kira. The five-loop master integrals are then evaluated numerically with the auxiliary mass flow method as implemented in AMFlow, in combination with an ad hoc interface to Kira. We obtain results for the fermionic contributions to the total semileptonic rate with an accuracy of more than thirty digits
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
Numerical evaluation of Mellin-Barnes integrals in Minkowskian regions and their application to two-loop bosonic electroweak contributions to the weak mixing angle of the Zbb(bar)-vertex
Full text linkIn der Z-Boson-Resonanzphysik sind mehrere Präzisionsobservablen in einem perfekten Zustand, bei dem die theoretische Unsicherheit niedriger ist als die gegenwärtige experimentelle Unsicherheit.
Das Konzept für den zukünftigen Teilchenbeschleuniger Future Circular Collider (FCC), will eine Verbesserung der Messungen für die Präzisionsobservablen um ein bis zwei signifikante Stellen erreichen.
Damit werden die Vorhersagen des elektroschwachen Standardmodells in eine Situation versetzt, in der vollständige Zweischleifenkorrekturen zusammen mit den führenden Dreischleifenkorrekturen obligatorisch werden.
2016 wurden die vollständigen Zweischleifenkorrekturen für den effektiven schwachen Mischungswinkel für die bottom Quarks sin^2/theta/^b_eff berechnet, indem die fehlenden bosonischen Zweischleifenkorrekturen bereitgestellt wurden.
Dabei liegt die Schwierigkeit in der Berechnung der entsprechenden Zwei-Schleifen Vertex-Feynman-Integrale, die mehrere massive Teilchen einschließen.
Gegenwärtig ist die analytische Rechnung der meisten dieser Integrale schwierig und deswegen werden rein numerische Techniken, mittels Sektorzerlegungsansatz und der Integralansatz nach Mellin-Barnes, angewandt.
Es war bis vor kurzem nicht bekannt, wie Mellin-Barnes-Integraldarstellungen in den minkowskischen Integrationsgebieten numerisch behandelt werden können.
Um dieses Problem anzugehen, stellen wir eine Vielzahl von ein- und mehrdimensionaler Techniken vor, die ein Teil des neuen Programms MBnumerics.m sind, welches in dieser Dissertation entwickelt wurde.
Der Sektorzerlegungsansatz und der Integralansatz nach Mellin-Barnes sind zusammen ausreichend, um elektroschwache Zweischleifenkorrekturen für die Präzisionsobservablen der Annihilation von e^+e^- in zwei Fermionen in der Z-Bosonresonanz auszurechnen.
Aktuell führt dies zu der genauesten Vorhersage für den effektiven elektroschwachen Mischungswinkel für bottom Quarks sin^2/theta/^b_eff = 0.232312.In the Z-boson resonance physics several precision observables are in a perfect state, where the theory uncertainty is lower than the present experimental uncertainty.
The ambitious concepts for the future collider, Future Circular Collider (FCC), aim for an improvement of measurements for the precision observables by one to two significant digits.
This will put the Electroweak Standard Model predictions in a situation where complete two-loop corrections together with the leading three-loop corrections will become mandatory.
The complete two-loop corrections for effective weak mixing angle for bottom quarks sin^2/theta/^b_eff were reported recently, by providing the missing bosonic two-loop corrections.
The difficult task in this computation is the calculation of the corresponding two-loop vertex Feynman integrals which include several massive particles.
At present the analytic evaluation for most of these integrals is out of reach and purely numerical techniques were applied.
Only two methods, sector decomposition approach and the Mellin-Barnes integral approach, are known to extract infrared and ultraviolet singularities in a systematic way for a general Feynman integral with fully automatized algorithms.
It was not known until recently how to treat Mellin-Barnes integral representations in Minkowskian regions numerically. To address this problem we introduce and discuss in detail a variety of one- and multi-dimensional techniques, which are part of a new program MBnumerics.m developed in this thesis work.
Two techniques, sector decomposition and Mellin-Barnes integral approach, are together sufficient to treat electroweak two-loop corrections to the precision observables for the e^+e^- annihilation into two fermions at the Z-boson resonance.
This leads to the most precise prediction at present for the effective weak mixing angle for bottom quarks: sin^2/theta/^b_eff=0.232312
Numerical evaluation of Mellin-Barnes integrals in Minowskian regions and their application to two-loop bosonic electroweak contributions to the weak mixing angle of the Zbb - vertex.
No full textn theZ-boson resonance physics several precision observables, like the mass andwidth of theZ-boson and the effective weak mixing angle for leptons and bot-tom quarks are in a perfect state, where the theory uncertainty is lower than thepresent experimental uncertainty. The ambitious concepts for the future colliders,like International Linear Collider (ILC), Future Circular Collider (FCC) or Circu-lar Electron-Positron Collider (CEPC), aim for an improvement of measurementsfor the precision observables by one to two significant digits. This will put the Elec-troweak Standard Model predictions in a situation where complete two-loop correc-tions together with the leading three-loop corrections will become mandatory. Thecomplete two-loop corrections for effective weak mixing angle for bottom quarks sin were reported recently, by providing the missingbosonictwo-loop correc-tions. The difficult task in this computation is the calculation of the correspond-ing two-loop vertex Feynman integrals which include several massive particles. Atpresent the analytic evaluation for most of these integrals is out of reach and purelynumerical techniques were applied. Only two methods are known to extract in-frared and ultraviolet singularities in a systematic way for a general Feynman inte-gral with fully automatized algorithms. Namely the sector decomposition approachand the Mellin-Barnes integral approach. It was not known until recently how totreat Mellin-Barnes integral representations in Minkowskian regions numerically.To address this problem we introduce and discuss in detail a variety of one- andmulti-dimensional techniques, which are part of a new programMBnumerics.mdeveloped in this thesis work. As a result, the Mellin-Barnes integral representa-tions of the two-loop vertex Feynman integrals can be evaluated numerically inEuclidean and Minkowskian regions with unprecedented accuracy. Furthermorethe two techniques, sector decomposition and Mellin-Barnes integral approach, arecomplementary and together sufficient to treat electroweak two-loop corrections tothe precision observables for the annihilation into two fermions at theZ-bosonresonance. This leads to the most precise prediction at present for the effective weakmixing angle for bottom quarks: sin = 0:232312
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
Kira and the block-triangular form
No full textFor many state-of-the-art cross section computations the standard approach of Feynman integral
reduction with the Laporta algorithm is the main bottleneck of the computation. We study a new
approach of Feynman integral reduction by introducing a block-triangular form, which is a smaller
system of equations compared to the system of equations which is generated with the Laporta
algorithm. The construction of the block-triangular form and its implementation in the program
Kira is the main interest of this report
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