13,138 research outputs found

    The static potential: lattice versus perturbation theory in a renormalon-based approach

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    We compare, for the static potential and at short distances, perturbation theory with the results of lattice simulations. We show that a renormalon-dominance picture explains why in the literature sometimes agreement, and another disagreement, is found between lattice simulations and perturbation theory depending on the different implementations of the latter. We also show that, within a renormalon-based scheme, perturbation theory agrees with lattice simulations.Comment: 18 pages, 11 figures, lattice data of Necco and Sommer introduced, references added, some lengthier explanations given, physical results unchange

    Model Independent Results for Heavy Quarkonium

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    We review a number of results for the spectrum and inclusive decays of heavy quarkonium systems which can be derived from QCD under well controlled approximations. They essentially follow from the hierarchy of scales in these systems, which can be efficiently exploited using non-relativistic effective field theories. In particular, we discuss under which conditions non-relativistic potential models emerge as effective theories of QCD.Comment: 15 pages. Invited brief revie

    The Mode of Computing

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    The Turing Machine is the paradigmatic case of computing machines, but there are others, such as Artificial Neural Networks, Table Computing, Relational-Indeterminate Computing and diverse forms of analogical computing, each of which based on a particular underlying intuition of the phenomenon of computing. This variety can be captured in terms of system levels, re-interpreting and generalizing Newell's hierarchy, which includes the knowledge level at the top and the symbol level immediately below it. In this re-interpretation the knowledge level consists of human knowledge and the symbol level is generalized into a new level that here is called The Mode of Computing. Natural computing performed by the brains of humans and non-human animals with a developed enough neural system should be understood in terms of a hierarchy of system levels too. By analogy from standard computing machinery there must be a system level above the neural circuitry levels and directly below the knowledge level that is named here The mode of Natural Computing. A central question for Cognition is the characterization of this mode. The Mode of Computing provides a novel perspective on the phenomena of computing, interpreting, the representational and non-representational views of cognition, and consciousness.Comment: 35 pages, 8 figure

    Renormalization group improvement of the NRQCD Lagrangian and heavy quarkonium spectrum

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    We complete the leading-log renormalization group scaling of the NRQCD Lagrangian at O(1/m2)O(1/m^2). The next-to-next-to-leading-log renormalization group scaling of the potential NRQCD Lagrangian (as far as the singlet is concerned) is also obtained in the situation mαs≫ΛQCDm\alpha_s \gg \Lambda_{QCD}. As a by-product, we obtain the heavy quarkonium spectrum with the same accuracy in the situation m\alpha_s^2 \simg \Lambda_{QCD}. When ΛQCDâ‰Șmαs2\Lambda_{QCD} \ll m\alpha_s^2, this is equivalent to obtain the whole set of O(mαs(n+4)ln⁥nαs)O(m\alpha_s^{(n+4)} \ln^n \alpha_s) terms in the heavy quarkonium spectrum. The implications of our results in the non-perturbative situation mαs∌ΛQCDm\alpha_s \sim \Lambda_{QCD} are also mentioned.Comment: 16 pages, LaTeX. Minor changes. Final versio

    Renormalization group improvement of the spectrum of Hydrogen-like atoms with massless fermions

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    We obtain the next-to-next-to-leading-log renormalization group improvement of the spectrum of Hydrogen-like atoms with massless fermions by using potential NRQED. These results can also be applied to the computation of the muonic Hydrogen spectrum where we are able to reproduce some known double logs at O(m\alpha^6). We compare with other formalisms dealing with log resummation available in the literature.Comment: 9 pages, LaTeX. Minor changes, note added, final versio

    Effective field theories for heavy quarkonium

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    We review recent theoretical developments in heavy quarkonium physics from the point of view of Effective Field Theories of QCD. We discuss Non-Relativistic QCD and concentrate on potential Non-Relativistic QCD. Our main goal will be to derive QCD Schr\"odinger-like equations that govern the heavy quarkonium physics in the weak and strong coupling regime. We also discuss a selected set of applications, which include spectroscopy, inclusive decays and electromagnetic threshold production.Comment: 162 pages, 30 figures, revised version, references added. Accepted for publication in Reviews of Modern Physic

    Synchronization in driven versus autonomous coupled chaotic maps

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    The phenomenon of synchronization occurring in a locally coupled map lattice subject to an external drive is compared to the synchronization process in an autonomous coupled map system with similar local couplings plus a global interaction. It is shown that chaotic synchronized states in both systems are equivalent, but the collective states arising after the chaotic synchronized state becomes unstable can be different in these two systems. It is found that the external drive induces chaotic synchronization as well as synchronization of unstable periodic orbits of the local dynamics in the driven lattice. On the other hand, the addition of a global interaction in the autonomous system allows for chaotic synchronization that is not possible in a large coupled map system possessing only local couplings.Comment: 4 pages, 3 figs, accepted in Phys. Rev.