Results 1 - 10 of 12039
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[en] Some properties of structure functions are found on the basis of perturbative QCD. These properties reflect the relation between sea quarks and gluons and, therefore, may be of a more general nature. The properties of several sets of phenomenological structure functions of a proton are analyzed, and it is shown that each set is in agreement with theoretical predictions in those regions of x and Q2 values where direct experimental data were used. Beyond the experimentally studied region, some deviations appear, which can be used to estimate the region of admissible extrapolation of the set under consideration until new experimental data become available. 13 refs., 6 figs
[en] We report on some results we get from fits of the Lopez-Yndurain parametrizations for structure functions to old CDHS and EMC data. These parametrizations are compatible with QCD, to leading order, at the end points and the relevant sum rules are properly imposed. (author)
[en] We first review a parton-language derivation of the photon structure function ''anomaly''. More recent higher order calculations show similar growth with Q2 at all x, and experimenters are urged to obtain enough data to separate the x and Q2 dependence. When this behavior is coupled with Bloom-Gilman duality, we find that the ''#betta# excitation'' form factors of the photon are expected to have different Q2 behavior from those of hadrons
[en] A family of multi-parameter, polynomially deformed oscillators (PDOs) given by the polynomial structure function ψ(n) is studied from the viewpoint of being (or not) in the class of Fibonacci oscillators. These obey the Fibonacci relation/property (FR/FP) meaning that the nth level energy En is given linearly, with real coefficients, by the two preceding ones En-1, En-2. We first prove that the PDOs do not fall in the Fibonacci class. Then, three different paths of generalizing the usual FP are developed for these oscillators: we prove that the PDOs satisfy the respective k-term generalized Fibonacci (or 'k-bonacci') relations; for these same oscillators we examine two other generalizations of the FR, the inhomogeneous FR and the 'quasi-Fibonacci' relation. Extended families of deformed oscillators are studied as well: the (q; μ)-oscillator with ψ(n) quadratic in the basic q-number [n]q is shown to obey the Tribonacci relation, while the (p, q; μ)-oscillators with ψ(n) quadratic (cubic) in the p, q-number [n]p,q are proven to obey the Pentanacci (Nine-bonacci) relations. Oscillators with general ψ(n), polynomial in [n]q or [n]p,q, are also studied.
[en] We calculate the first moment of the photon structure function, < x>γ=∫01dxF2γ(x,Q2), on the quenched lattices with β=6.0 using the formalism developed by the authors recently. In this exploratory study, we take into account only the connected contractions. The result is compared with the experimental data as well as model predictions
[en] If a nucleus is regarded as a collection of quasi-free nucleons, the nuclear structure functions are simply proportional to the corresponding structure functions of the nucleon. It has been argued that the conventional picture of the nucleus might not hold when the nucleus is probed during a very short time. A simple parton model has been formulated, illustrating the idea of an anomalous behaviour of nuclear structure functions. The nucleus is pictured as one bag of partons
[en] It is a great challenge of modern physics to understand the rich spectroscopy of hadrons in terms of quarks and gluons. Today we believe that QCD is the underlying theory but unfortunately no full solution of its field equations is known. Hence all investigations on the structure of hadrons rely on some model. In particular non-relativistic models have been successfully applied. The concept of a quark-antiquark potential being the basis of such models can only be justified in the limit of heavy quarks. However, surprisingly good results are also obtained for relatively light quark systems. The experimentally known meson spectra offer the possibility to determine the quark-antiquark potential. In the literature many analyses of the meson spectra are reported using phenomenological or semiphenomenological quark-antiquark potentials. The parameters are adjusted in order to fit the meson masses and sometimes the leptonic widths. Following the qualitative results of lattice gauge calculations and perturbation theory almost all potentials contain a Coulombic term at small distances and are monotonically increasing at large distances. However, all calculations use rather restricted forms of the potential thereby introducing a bias into its shape. In this contribution we want to apply the exact inverse spectrum method as introduced by Thacker et al. for s-state mesons. This method has been used to analyse charmonium which was the most suitable known qantiq-system at that time. It is obvious that the inversion based on only two states cannot give a good reproduction of the confinement potential. Here, we analyse the bantib-system which is the best suited one today. The bantib-system has not only a rich known spectrum but because of the heavy b-quark it is the least relativistic quark system
[en] Perturbative calculations of factorized physical quantities, such as moments of structure functions, suffer from renormalization- and factorization-scheme dependence. The application of the principle of minimal sensitivity to “optimize” the scheme choices is reconsidered, correcting deficiencies in the earlier literature. The proper scheme variables, RG equations, and invariants are identified. Earlier results of Nakkagawa and Niégawa are recovered, even though their starting point is, at best, unnecessarily complicated. In particular, the optimized coefficients of the coefficient function C are shown to vanish, so that . The resulting simplifications mean that the optimization procedure is as simple as that for purely-perturbative physical quantities.