Sense and Nonsense on Parton Distribution functions of the Photon

The organization of finite order QCD approximations to $F_2^{\gamma}(x,Q^2)$ based on the separation of pure QED contribution from those of genuine QCD nature is discussed.Comment: Talk given at the International Symposium PHOTON 2007, Paris, July 2007, 4 pages and 1 figure, references correcte

Direct vs. resolved photon: an exercise in factorization

Direct and resolved photon interactions are shown to be intimately related through the factorization mechanism. It is argued that in theoretically consistent analysis of jet production in $\gamma$p and ep collisions the LO resolved $\gamma$ contribution must be considered together with the NLO direct $\gamma$ component. Recent data from HERA therefore do not provide a direct evidence for the former component, but should rather be interpreted as a manifestation of the $O(\alpha\alpha_s^2)$ term in $\gamma$p and, via the Weizs\"acker-Williams approximation, in ep interactions.Comment: PRA-HEP/93-07, Latex, 10 pages and 5 Postscript figures in 2 PS files appended at the end of Tex fil

On an asymptotic estimate of the nn-loop correction in perturbative QCD

A recently proposed method of estimating the asymptotic behaviour of QCD perturbation theory coefficients is critically reviewed and shown to contain numerous invalid mathematical operations and unsubstantiated assumptions. We discuss in detail why this procedure, based solely on renormalization group (RG) considerations and analyticity constraints, cannot lead to such estimates. We stress the importance of correct renormalization scheme (RS) dependence of any meaningful asymptotic estimate and argue that the unambiguous summation of QCD perturbation expansions for physical quantities requires information from outside of perturbation theory itself.Comment: PRA-HEP-92/17, Latex, 20 pages of text plus 5 figures contained in 5 separate PS files. Four of them (corresponding to Figs.1,2,3,5) are appended at the end of this file, the (somewhat larger one) corresponding to Fig.4 can be obtained from any of the mentioned E-mail addresses upon request. E-mail connections: J. Chyla - [email protected]) or h1kchy@dhhdesy3 P. Kolar - [email protected]

Electroproduction Cross Section of Large_Et Hadrons at NLO and Virtual Photon Structure Function

We calculate Higher Order corrections to the resolved component of the electroproduction cross section of large-Et hadrons. The parton distributions in the virtual photon are studied in detail and a NLO parametrization of the latter is proposed. The contribution of the resolved component to the forward production of large-Et hadrons is calculated and its connection with the BFKL cross section is discussed.Comment: Latex, 32 pages with 6 figure

On QCD analysis of stucture function F2γF_2^{\gamma} in alternative approach

The alternative approach to QCD analysis of the photon structure function $F_2^{\gamma}$ is presented. It differs from the conventional one by the presence of the terms which in conventional approach appear in higher orders. We show that this difference concerns also the photonic parton distribution functions. In the alternative approach, the complete LO analysis of $F_2^{\gamma}$ can be performed as all required quantities are known. At the NLO, however, one of the coefficient function is so far not available and thus only the photonic parton distribution function can be computed and compared to those of standard approach. We discuss the numerical difference of these approaches at the LO and the NLO approximation and show that in case of $F_2^{\gamma}$ this difference is non-negligible and may play an important role in the analysis on photon data of the future experiments.Comment: 25 page

On parton distributions beyond the leading order

The importance of properly taking into account the factorization scheme dependence of parton distribution functions is emphasized. A serious error in the usual handling of this topic is pointed out and the correct procedure for transforming parton distribution functions from one factorisation scheme to another recalled. It is shown that the conventional $\overline{\rm {MS}}$ and DIS definitions thereof are ill-defined due to the lack of distinction between the factorisation scheme dependence of parton distribution functions and renormalisation scheme dependence of the strong coupling constant $\alpha_s$. A novel definition of parton distribution functions is suggested and its role in the construction of consistent next-to-leading order event generators briefly outlined.Comment: PRA-HEP-93/05, Latex, 10 pages and 2 Postscript figures appended at the end of this fil

QCD improved parton distribution functions of γL∗{\mathbf{\gamma^*_L}}

QCD corrections to the QED formula for parton distribution functions of the longitudinal virtual photon are derived in the leading--logarithmic approximation. It is shown that the resulting PDF satisfy the same homogeneous evolution equations as those of hadrons, but contrary to the latter are perturbatively calculable. Properties of these distribution functions are discussed and their phenomenological consequences outlined.Comment: 9 pages, Latex, 5 figures in eps forma

Automatizované metody popisu struktury odborného textu a vztah některých prvků ke kvalitě textu

Universal Semantic Language (USL) is a semi-formalized approach for the description of knowledge (a knowledge representation tool). The idea of USL was introduced by Vladimir Smetacek in the system called SEMAN which was used for keyword extraction tasks in the former Information centre of the Czechoslovak Republic. However due to the dissolution of the centre in early 90's, the system has been lost. This thesis reintroduces the idea of USL in a new context of quantitative content analysis. First we introduce the historical background and the problems of semantics and knowledge representation, semes, semantic fields, semantic primes and universals. The basic methodology of content analysis studies is illustrated on the example of three content analysis tools and we describe the architecture of a new system. The application was built specifically for USL discovery but it can work also in the context of classical content analysis. It contains Natural Language Processing (NLP) components and employs the algorithm for collocation discovery adapted for the case of cooccurences search between semantic annotations. The software is evaluated by comparing its pattern matching mechanism against another existing and established extractor. The semantic translation mechanism is evaluated in the task of...Univerzální sémantický jazyk (USJ) je semi-formalizovaný způsob zápisu znalostí (systém pro reprezentaci znalostí). Myšlenka USJ byla rozvinuta Vladimírem Smetáčkem v 80. letech při pracech na systému SÉMAN (Universální semantický analyzátor). Tento systém byl využíván pro automatizovanou extrakci klíčových slov v tehdejším informačním centru ČSSR. Avšak se zánikem centra v 90. letech byl systém SEMAN ztracen. Tato dizertace oživuje myšlenku USJ v novém kontextu automatizované obsahové analýzy. Nejdříve prezentujeme historický kontext a problémy spojené s reprezentací znalostí, sémů, sémantických polí, sémantických primitivů a univerzálií. Dále je představena metodika kvantitativní obsahové analýzy na příkladu tří klasických aplikací. Podrobně popíšeme architekturu nové aplikace, která byla vyvinuta speciálně pro potřeby evaluace USJ. Program může fungovat jako nástroj pro klasickou obsahovou analýzu, avšak obsahuje i nástroje pro zpracování přirozeného jazyka (NLP) a využívá algoritmů pro vyhledávání kolokací. Tyto byly upraveny pro potřeby vyhledávání vazeb mezi sémantickými anotacemi. Jednotlivé součásti programu jsou podrobeny praktickým testům. Subsystém pro vyhledávní vzorů v textech je porovnán s existujícím extraktorem klíčových slov. Mechanismus pro překlad do sémantických kódů je...Institute of Information Studies and LibrarianshipÚstav informačních studií a knihovnictvíFilozofická fakultaFaculty of Art