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Search Results: 1 - 10 of 528039 matches for " D. Müller "
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Calculation of higher-twist evolution kernels for polarized deep inelastic scattering
D. Müller
Physics , 1997, DOI: 10.1016/S0370-2693(97)00722-3
Abstract: Based on the non-local light-ray operator technique, we develop an algorithm for the computational calculation of evolution kernels for higher-twist operators in leading order of the perturbation theory. We compute the evolution kernel for the twist-3 operators in the flavour singlet channel. Our result confirms the local anomalous dimensions computed by Bukhvostov, Kuraev, and Lipatov as well as the non-local evolution kernels of Balitzky and Braun.
The Parton Distribution Functions in the Limit $x_{Bj}\to 1$
D. Müller
Physics , 1994,
Abstract: We review both the counting rule and the influence of the evolution in $Q^2$ for the large $x_{Bj}$ behaviour of the valance quark distribution functions. Based on a factorization procedure we present a more general perturbative treatment to compute this behaviour. A complete analysis is performed in the scalar $\phi^3_{[6]}$-theory for the parton distribution function of the ``meson'', which shows that logarithmical corrections arise from the distribution amplitude and that the reference momentum square $Q_0^2$ is fixed by $x_{Bj}$.
Extraction of skewed parton distributions
D. Müller
Physics , 2000,
Abstract: Skewed parton distributions contain new non-perturbative information about hadronic states. Thus, their extraction from experimental data is an important goal. Properties and models for skewed parton distributions as well as their extraction, based on perturbative leading-order results, are shortly reviewed.
Scheme dependence of NLO corrections to exclusive processes
D. Müller
Physics , 1998, DOI: 10.1103/PhysRevD.59.116003
Abstract: We apply the so-called conformal subtraction scheme to predict perturbatively exclusive processes beyond leading order. Taking into account evolution effects, we study the scheme dependence for the photon-to-pion transition form factor and the electromagnetic pion form factor at next-to-leading order for different pion distribution amplitudes. Relying on the conformally covariant operator product expansion and using the known higher order results for polarized deep inelastic scattering, we are able to predict perturbative corrections to the hard-scattering amplitude of the photon-to-pion transition form factor beyond next-to-leading order in the conformal scheme restricted to the conformal limit of the theory.
Restricted conformal invariance in QCD and its predictive power for virtual two-photon processes
D. M{ü}ller
Physics , 1997, DOI: 10.1103/PhysRevD.58.054005
Abstract: The conformal algebra provides powerful constraints, which guarantee that renormalized conformally covariant operators exist in the hypothetical conformal limit of the theory, where the $\beta$-function vanishes. Thus, in this limit also the conformally covariant operator product expansion on the light cone holds true. This operator product expansion has predictive power for two-photon processes in the generalized Bjorken region. Only the Wilson coefficients and the anomalous dimensions that are known from deep inelastic scattering are required for the prediction of all other two-photon processes in terms of the process-dependent off-diagonal expectation values of conformal operators. It is checked that the next-to-leading order calculations for the flavour non-singlet meson transition form factors are consistent with the corrections to the corresponding Wilson coefficients in deep inelasitic scattering.
Does Soil Disturbance Affect Soil Phosphorus Fractions?  [PDF]
Yonathan D. Redel, Rudolf Schulz, Torsten Müller
Open Journal of Soil Science (OJSS) , 2013, DOI: 10.4236/ojss.2013.36031

Increased turnover of organic matter as a result of soil disturbance (e.g. by soil tillage) is described in principle, but the direct influence of soil disturbance on soil P turnover especially for organic farming systems has not been sufficiently proven. The objective of the study was to evaluate the short term effect of soil disturbance on different soil P fractions in a soil shaking experiment. Four soils were incubated for 10 days in the dark with three different disturbance treatments: 1) no disturbance, 2) overhead shaking for 2 h at the beginning of the experiment and 3) continuous overhead shaking at 5 r. p. m. The four investigated soils were: 1) a silty loam soil with long term bio-compost application and 2) the corresponding soil without bio-compost application, 3) a long-term organically managed clay loam soil and 4) a clay loam soil with long time application of pig manure, all not and from Baden-Württemberg, Germany. We determined NaHCO3-, NaOH- and H2SO4-extractable inorganic and organic P fractions (Pi and Po, resp.) in a sequential extraction. Furthermore, the potentially plant available P as Calcium-acetate-lactate-extractable P (CAL-P) and P extractable by electro-ultra-filtration (EUF-P), and aqua regia extractable total P (PT) were determined. Furthermore, we determined microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), and acid phosphatase activity in soil. The organically managed soil had the highest PT contents (1300 mg·kg-1). The soil with pig manure application had the smallest potentially labile P fractions (NaHCO3-Pi and -Po and NaOH-Pi). The ecologically managed soil had the biggest organic P fractions (114 mg·kg-1 NaHCO3-Po and 463 mg·kg-1 NaOH-Po), but, this soil was the lowest in CAL-P (5 mg·kg-1). Short term soil

Exclusive processes in position space and the pion distribution amplitude
Braun, V.;Müller, D.
High Energy Physics - Phenomenology , 2007, DOI: 10.1140/epjc/s10052-008-0608-4
Abstract: We suggest to carry out lattice calculations of current correlators in position space, sandwiched between the vacuum and a hadron state (e.g. pion), in order to access hadronic light-cone distribution amplitudes (DAs). In this way the renormalization problem for composite lattice operators is avoided altogether, and the connection to the DA is done using perturbation theory in the continuum. As an example, the correlation function of two electromagnetic currents is calculated to the next-to-next-to-leading order accuracy in perturbation theory and including the twist-4 corrections. We argue that this strategy is fully competitive with direct lattice measurements of the moments of the DA, defined as matrix elements of local operators, and offers new insight in the space-time picture of hard exclusive reactions.
Verringerung des Parameterraums von IP unter Verwendung von Parameterabh ngigkeiten
V. Jerini?,D. Müller
Advances in Radio Science : Kleinheubacher Berichte , 2003,
Abstract: Um eine Wiederverwendung in verschiedenen Anwendungen zu erm glichen, verfügen Intellectual Properties (IP) h ufig über einen umfangreichen Parametersatz. Auf der einen Seite erlaubt die extensive Verwendung von Parametern die Anpassung von IP an verschiedene Spezifikationen. Andererseits vergr ert jeder Parameter den Parameterraum, wodurch es praktisch unm glich wird, die korrekte Funktion der IP für alle Parameterkombinationen zu verifizieren. Es wird eine Methode vorgestellt, die, basierend auf vorgegebenen Abh ngigkeiten der Parameter untereinander, den Parameterraum in orthogonale Subr ume, sogenannte Parameter-Dom nen, unterteilt, wobei ungültige Parameterkombinationen entfernt werden. Durch diesen Schritt kann der Parameterraum zum Teil erheblich verkleinert werden. Durch die Verwendung von orthogonalen Subr umen werden Verifikationsumgebungen, wie z.B. Specman EliteTM von Verisity, die Stimuli und Parameterzuweisungen pseudozuf llig erzeugen k¨onnen, wirkungsvoll unterstützt, indem mehrfache Simulationen gleichwertiger Zuweisungen verhindert werden. In order to be reused in different applications IP are usually parameterized.While a rich parameter set enables users to customize IP to their needs, verification complexity is increased by enlarging the parameter space with every additional parameter. In this work, a graph-based approach to splitting the parameter space into orthogonal subspaces on the basis of defined parameter interdependences is proposed. By utilizing so-called parameter domain graphs, invalid parameter configurations are removed from the parameter space. Verification environments with the capability to automatically generate pseudo-random parameter combinations, e.g. Specman EliteTM von Verisity, may create parameter combinations which are virtually equal. This can be avoided by using orthogonal subspaces.
Predictions for deeply virtual Compton scattering on a spin-one target
A. Kirchner,D. Müller
Physics , 2002,
Abstract: We consider hard leptoproduction of a photon on a spin-one target and give the general azimuthal angular dependence of the differential cross section. Furthermore, we estimate the beam spin asymmetry for an unpolarized deuteron target at HERMES.
Evolution Kernels of Twist-3 Light-Ray Operators in Polarized Deep Inelastic Scattering
B. Geyer,D. Müller,D. Robaschik
Physics , 1996, DOI: 10.1016/S0920-5632(96)90013-4
Abstract: The twist three contributions to the $Q^2$-evolution of the spin-dependent structure function $g_2(x)$ are considered in the non-local operator product approach. Starting from the perturbative expansion of the T-product of two electromagnetic currents, we introduce the nonlocal light-cone expansion proved by Anikin and Zavialov and determine the physical relevant set of light-ray operators of twist three. Using the equations of motion we show the equivalence of these operators to the Shuryak-Vainshtein operators plus the mass operator, and we determine their evolution kernels using the light-cone gauge with the Leibbrandt-Mandelstam prescription. The result of Balitsky and Braun for the twist three evolution kernel (nonsinglet case) is confirmed.
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