1,354,190 research outputs found
Theoretical and phenomenological aspects of vector boson production
No full textThe production of three gauge bosons in high-energy collisions - in particular in view of a next-linear collider with center of mass energies in the TeV range - offers an unique opportunity to probe the Standard Model (SM) of today's particle physics. In this thesis we pay particular attention to the electroweak sector of the theory. We investigate the gauge structure {i. e. possible deviations from the SM predictions of gauge boson self-interactions manifest e. g. in anomalous quartic gauge boson couplings and Radiation zeros) as well as electroweak radiative corrections in order to improve theoretical predictions for SM processes. Quartic gauge boson couplings can be regarded as a direct window on the sector of electroweak symmetry breaking. We have studied the impact of three such anomalous couplings on the processes e+e(^-) → WWγ, ZZγ and Zγγ at LEP2 and a future linear collider. In certain high-energy scattering processes involving charged particles and the emission of one or more photons, the scattering amplitude vanishes for particular configurations of the final state particles. The fact that gauge symmetry is a vital ingredient for the cancellation to occur means that radiation zeros can be used to probe physics beyond the standard model. For example anomalous electroweak gauge boson couplings destroy the delicate cancellation necessary for the zero to occur. We have studied the process qq → WWγ. To match the expected experimental precision at future linear colliders, improved theoretical predictions beyond next-to-leading order are required. By choosing an appropriate gauge, we have developed a formalism to calculate such corrections for arbitrary electroweak processes. As an example we consider here the processes e(^+)e → f f and e(^+)e(^-) → W(^+)(_T)W(^-)(_T), W(^+)(_L)W(^-)(_L) and study the perturbative structure of the electroweak Sudakov logarithms by means of an explicit two-loop calculation. In this way we investigate how the Standard Model, with its mass gap between the photon and Z boson in the neutral sector, compares to unbroken theories like QED and QCD. We observe that the two-loop corrections are consistent with an exponentiation of the one-loop corrections. In this sense the Standard Model behaves like an unbroken theory at high energies
Status of electroweak corrections to top pair production
No full textFleischer J, Leike A, Riemann T, Werthenbach A. Status of electroweak corrections to top pair production. 2002
Massive two-loop Bhabha scattering - the factorizable subset
No full textFleischer J, Riemann T, Tarasov OV, Werthenbach A. Massive two-loop Bhabha scattering - the factorizable subset. NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS. 2003;116:43-47.The experimental precision that will be reached at the next generation of colliders makes it indispensable to improve theoretical predictions significantly. Bhabha scattering (e(+)e(-) --> e(+)e(-)) is one of the prime processes calling for a better theoretical precision, in particular for non-zero electron masses. We present a first subset of the full two-loop calculation, namely the factorizable subset. Our calculation is based on DIANA [1]. We reduce tensor integrals to scalar integrals in shifted (increased) dimensions and additional powers of various propagators, so-called dots-on-lines. Recurrence relations [2,3] remove those dots-on-lines as well as genuine dots-on-lines (originating from mass renormalization) and reduce the dimension of the integrals to the generic d = 4 - 2epsilon dimensions. The resulting master integrals have to be expanded to O(epsilon) to ensure proper treatment of all finite terms
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Factorizing one-loop contributions to two-loop Bhabha scattering and automatization of Feynman diagram calculations
No full textFleischer J, Tarasov O, Riemann T, Werthenbach A. Factorizing one-loop contributions to two-loop Bhabha scattering and automatization of Feynman diagram calculations. In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT. Vol 502. ELSEVIER SCIENCE BV; 2003: 567-569.In higher order calculations a number of new technical problems arise: one needs diagrams in arbitrary dimension in order to obtain their needed epsilon-expansion, zero Gram determinants appear, renormalization produces diagrams with 'dots' on the lines, i.e. higher-order powers of scalar propagators. All these problems cannot be accessed by the 'standard' Passarino-Veltman approach: what is needed for higher loops is not available there. We demonstrate our method of how to solve these problems. (C) 2003 Elsevier Science B.V. All rights reserved
Inferring Log-Based Behavioural System Models using Markov Chains
No full textAn essential step of software development is obtaining an understanding of the behaviour of a system. Accurate state models of system behaviour might help software developers build such an understanding. There exist several techniques for automatically inferring models on system behaviour using log analysis, but these do not scale well for systems that produce large amounts of logs.In this study, we present an approach for inferring concise state models of system behaviour using log analysis, called MASM (Markov Algorithm for inferring concise State Models), which implements a Markov chain. We argue this approach has the potential for higher scalability than existing techniques, as it attempts to approximate a state model by exploiting the properties of Markov chains. This is achieved by considering a sequence of log statements as a stochastic process, which enables MASM to infer a naive state model from a set of log statements, which is then minimized using the properties of Markov chains.We evaluated MASM in an empirical study on the XRP Ledger Consensus Protocol. In this empirical study, MASM was evaluated on accuracy at different compression rates, and scalability. The results indicate that MASM shows several knee points in terms of accuracy, suggesting several optimal compression rates. We also found that the run-time of MASM scales linearly with the size of the dataset. Finally, we discovered that MASM is unable to outperform a random compression algorithm, which compresses the model by randomly merging states, in terms of accuracy. However, further research is required on measuring the readability of the produced models to derive definitive conclusions on the performance of MASM compared to a random compression algorithm.CSE3000 Research ProjectComputer Science and Engineerin
Variations on the Author
No full text“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
No full textWe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Electroweak one-loop corrections for e(+)e(-) annihilation into t(t)over-bar including hard bremsstrahlung
No full textFleischer J, Leike A, Riemann T, Werthenbach A. Electroweak one-loop corrections for e(+)e(-) annihilation into t(t)over-bar including hard bremsstrahlung. EUROPEAN PHYSICAL JOURNAL C. 2003;31(1):37-56.We present the complete electroweak one-loop corrections to top-pair production at a linear e(+)e(-) collider in the continuum region. Besides weak and photonic virtual corrections, real hard bremsstrahlung with simple realistic kinematical cuts is included. For the bremsstrahlung we advocate a semi-analytical approach with a high numerical accuracy. The virtual corrections are parameterized through six independent form factors, suitable for Monte Carlo implementation. Alternatively, our numerical package Topfit, a stand-alone code, can be utilized for the calculation of both differential and integrated cross sections as well as forward-backward asymmetries
- …
