1,218 research outputs found
Comment on the Average Momentum of Top Quarks in the Threshold Region
The behavior of the momentum distribution of top quarks in the threshold
region is investigated. The qualitative behavior, in particular the dependence
of the average momentum on the strong coupling constant can be understood from
analytical calculations for the Coulomb potential. Ambiguities in the relation
between the excitation curve and the top mass are addressed.Comment: Univ. of Karlsruhe preprint TTP93-31, LaTeX, 6 pages including two
figures (uses epsf) appended as uuencoded postscript fil
Polarization in Top Quark Production and Decay near Threshold
Theoretical results are presented for top quarks produced in annihilation of
polarized electrons on positrons. Polarization studies for pairs near
threshold are free from hadronization ambiguities. This is due to the short
lifetime of the top quark. Semileptonic decays are discussed as well as their
applications in studying polarization dependent processes involving top quarks.
The Green function formalism is applied to production at future
colliders with polarized beams. Lippmann--Schwinger equation is solved
numerically for the QCD chromostatic potential given by the two-loop formula at
large momentum transfers and Richardson ansatz at intermediate and small ones.
The polarization dependent momentum distributions of top quarks and their decay
products are calculated.Comment: 6 pages, LaTex (uses epsf.sty, 2 figures appended as uuencoded ps
files). The complete paper, including figures, is also available via
anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as
/ttp94-24/ttp94-24.ps, or via www at
http://ttpux2.physik.uni-karlsruhe.de/preprints.html
Exclusive and photoproduction and the low gluon
We study exclusive vector meson photoproduction, with
or , at NLO in collinear factorisation, in order to
examine what may be learnt about the gluon distribution at very low . We
examine the factorisation scale dependence of the predictions. We argue that,
using knowledge of the NLO corrections, terms enhanced by a large
can be reabsorbed in the LO part by a choice of the factorisation scale. (In
these exclusive processes takes the role of Bjorken-.) Then, the scale
dependence coming from the remaining NLO contributions has no
enhancements. As a result, we find that predictions for the amplitude of
production are stable to within about . This will allow
data for the exclusive process at the LHC, particularly
from LHCb, to be included in global parton analyses to constrain the gluon PDF
down to . Moreover, the study of exclusive
photoproduction indicates that the gluon density found in the recent global PDF
analyses is too small at low and low scales.Comment: 21 pages, 6 figures. Text significantly improved, references added,
version to be published in J.Phys.
Privacy in the Sharing Economy
Contemporary C2C platforms, such as Airbnb, have exhibited considerable growth in recent years and are projected to continue doing so in the future. These novel consumer-to-consumer marketplaces have started to obliterate the boundaries between private and economic spheres. Marketing personal resources online is inherently associated with the disclosure of personal and sometimes intimate information. This raises unprecedented questions of privacy. Yet, there is so far little research on the role of privacy considerations in the sharing economy literature. Leveraging the theoretical perspective of privacy calculus, we address this gap by investigating how privacy concerns and economic prospects shape a potential provider’s intentions to share via different communication channels. We relate privacy concerns back to the provider’s perceptions of the audience. We evaluate our research model by means of a scenario-based online survey, providing broad support for our reasoning
Massive Quark Production in Electron Positron Annihilation to Order
Recent analytical and numerical results for the three-loop polarization
function allow to present a phenomenological analysis of the cross section for
massive quark production in electron positron annihilation to order
. Numerical predictions based on fixed order perturbation theory
are presented for charm and bottom production above 5 and 11.5 GeV,
respectively. The contribution from these energy regions to ,
the running QED coupling constant at scale M_Z, are given. The dominant terms
close to threshold, i.e. in an expansion for small quark velocity , are
presented.Comment: 26 pages (Latex), 16 figures (Postscript
MonetDB/XQuery: a fast XQuery processor powered by a relational engine
Relational XQuery systems try to re-use mature relational data management infrastructures to create fast and scalable XML database technology. This paper describes the main features, key contributions, and lessons learned while implementing such a system. Its architecture consists of (i) a range-based encoding of XML documents into relational tables, (ii) a compilation technique that translates XQuery into a basic relational algebra, (iii) a restricted (order) property-aware peephole relational query optimization strategy, and (iv) a mapping from XML update statements into relational updates. Thus, this system implements all essential XML database functionalities (rather than a single feature) such that we can learn from the full consequences of our architectural decisions. While implementing this system, we had to extend the state-of-the-art with a number of new technical contributions, such as loop-lifted staircase join and efficient relational query evaluation strategies for XQuery theta-joins with existential semantics. These contributions as well as the architectural lessons learned are also deemed valuable for other relational back-end engines. The performance and scalability of the resulting system is evaluated on the XMark benchmark up to data sizes of 11GB. The performance section also provides an extensive benchmark comparison of all major XMark results published previously, which confirm that the goal of purely relational XQuery processing, namely speed and scalability, was met
The Economics of Multi-Hop Ride Sharing - Creating New Mobility Networks Through IS
Ride sharing allows to share costs of traveling by car, e.g., for fuel or highway tolls. Furthermore, it reduces congestion and emissions by making better use of vehicle capacities. Ride sharing is hence beneficial for drivers, riders, as well as society. While the concept has existed for decades, ubiquity of digital and mobile technology and user habituation to peer-to-peer services and electronic markets have resulted in particular growth in recent years. This paper explores the novel idea of multi-hop ride sharing and illustrates how information systems can leverage its potential. Based on empirical ride sharing data, we provide a quantitative analysis of the structure and the economics of electronic ride sharing markets. We explore the potential and competitiveness of multi-hop ride sharing and analyze its implications for platform operators. We find that multi-hop ride sharing proves competitive against other modes of transportation and has the potential to greatly increase ride availability and city connectedness, especially under high reliability requirements. To fully realize this potential, platform operators should implement multi-hop search, assume active control of pricing and booking processes, improve coordination of transfers, enhance data services, and try to expand their market share
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