Results 1 - 10 of 12191
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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 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 ''ß excitation'' form factors of the photon are expected to have different Q2 behavior from those of hadrons
[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] When a flux-limited quasar sample is observed at later times, there will be more dimmed quasars than brightened ones, due to a selection bias induced at the time of sample selection. Quasars are continuously varying and there are more fainter quasars than brighter ones. At the time of selection, even symmetrical variability will result in more quasars with their instantaneous fluxes scattered above the flux limit than those scattered below, leading to an asymmetry in flux changes over time. The same bias would lead to an asymmetry in the ensemble structure function (SF) of the sample such that the SF based on pairs with increasing fluxes will be slightly smaller than that based on pairs with decreasing fluxes. We use simulated time-symmetric quasar light curves based on the damped random walk prescription to illustrate the effects of this bias. The level of this bias depends on the sample, the threshold of magnitude changes, and the coverage of light curves, but the general behaviors are consistent. In particular, the simulations matched to recent observational studies with decade-long light curves produce an asymmetry in the SF measurements at the few percent level, similar to the observed values. These results provide a cautionary note on the reported time asymmetry in some recent quasar variability studies.
[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] The establishment of effective null models can provide reference networks to accurately describe statistical properties of real-life signed networks. At present, two classical null models of signed networks (i.e., sign and full-edge randomized models) shuffle both positive and negative topologies at the same time, so it is difficult to distinguish the effect on network topology of positive edges, negative edges, and the correlation between them. In this study, we construct three refined edge-randomized null models by only randomizing link relationships without changing positive and negative degree distributions. The results of nontrivial statistical indicators of signed networks, such as average degree connectivity and clustering coefficient, show that the position of positive edges has a stronger effect on positive-edge topology, while the signs of negative edges have a greater influence on negative-edge topology. For some specific statistics (e.g., embeddedness), the results indicate that the proposed null models can more accurately describe real-life networks compared with the two existing ones, which can be selected to facilitate a better understanding of complex structures, functions, and dynamical behaviors on signed networks. (paper)
[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