921,641 research outputs found

    Nonperturbative physics at short distances

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    There is accumulating evidence in lattice QCD that attempts to locate confining fields in vacuum configurations bring results explicitly depending on tha lattice spacing (that is, ultraviolet cut off). Generically, one deals with low-dimensional vacuum defects which occupy a vanishing fraction of the total four-dimensional space. We review briefly existing data on the vacuum defects and their significance for confinement and other nonperturbative phenomena. We introduce the notion of `quantum numbers' of the defects and draw an analogy, rather formal one, to developments which took place about 50 years ago and were triggered by creation of the Sakata model.Comment: 15 pages, contributed to International Symposium on the Jubilee of the Sakata Model (pnLambda50), Nagoya, Japan, Nov. 200

    Power corrections from short distances

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    It is argued that power contributions of short distance origin naturally arise in the infrared finite coupling approach. A phenomenology of 1/Q21/Q^2 power corrections is sketched.Comment: 5 pages, latex, no figures. Expanded version of a talk presented at the EPS HEP97 Conference (Jerusalem, August 1997

    Quark Pseudo-Distributions at Short Distances

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    We perform a one-loop study of the small-z32z_3^2 behavior of the Ioffe-time distribution (ITD) M(Îœ,z32){\cal M} (\nu, z_3^2), the basic function that may be converted into parton pseudo- and quasi-distributions. We calculate the corrections at the operator level, so that our results may be later used for pseudo-distribution amplitudes and generalized parton pseudo-distributions. We separate two sources of the z32z_3^2-dependence at small z32z_3^2. One is related to the ultraviolet (UV) singularities generated by the gauge link, and another to short-distance logarithms generating perturbative evolution of parton densities. Our calculation explicitly shows that, for a finite UV cut-off, the UV-singular terms vanish when z32=0z_3^2=0. The UV divergences are absent in the ratio M(Îœ,z32)/M(0,z32){\cal M} (\nu, z_3^2)/{\cal M} (0, z_3^2) ("reduced" ITD). Still, it has a non-trivial short-distance behavior due to ln⁥z32Λ2\ln z_3^2 \Lambda^2 terms generating perturbative evolution of the parton densities. We give an explicit expression, up to constant terms, for the reduced ITD at one loop. It may be used in extraction of PDFs from the lattice QCD simulations. We also use our results to get new insights concerning the structure of parton quasi-distributions at one-loop level.Comment: 10 pages, 4 figures, typos fixed, references added, some changes in tex

    Short distances, black holes, and TeV gravity

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    The Hawking effect can be rederived in terms of two-point functions and in such a way that it makes it possible to estimate, within the conventional semiclassical theory, the contribution of ultrashort distances at I+I^+ to the Planckian spectrum. Thermality is preserved for black holes with ÎșlP<<1\kappa l_P << 1. However, deviations from the Planckian spectrum can be found for mini black holes in TeV gravity scenarios, even before reaching the Planck phase.Comment: 4 pages. Contribution to the MG11 Meeting (Berlin, July 2006

    Dynamical nucleus-nucleus potential at short distances

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    The dynamical nucleus-nucleus potentials for fusion reactions 40Ca+40Ca, 48Ca+208Pb and 126Sn+130Te are studied with the improved quantum molecular dynamics (ImQMD) model together with the extended Thomas-Fermi approximation for the kinetic energies of nuclei. The obtained fusion barrier for 40Ca+40Ca is in good agreement with the extracted fusion barrier from the measured fusion excitation function, and the depth of the fusion pockets are close to the results of time-dependent Hartree-Fock calculations. The energy dependence of fusion barrier is also investigated. For heavy fusion system, the fusion pocket becomes shallow and almost disappears for symmetric systems and the obtained potential at short distances is higher than the adiabatic potential.Comment: 6 figures, accepted for publication in Phys. Rev.

    Monopole clusters at short and large distances

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    We present measurements of various geometrical characteristics of monopole clusters in SU(2) lattice gauge theory. The maximal Abelian projection is employed and both infinite, or percolating cluster and finite clusters are considered. In particular, we observe scaling for average length of segments of the percolating cluster between self-crossings, correlators of vacuum monopole currents, angular correlation between links along trajectories. Short clusters are random walks and their spectrum in length corresponds to free particles. At the hadronic scale, on the other hand, the monopole trajectories are no longer random walks. Moreover, we argue that the data on the density of finite clusters suggest that there are long-range correlations between finite clusters which can be understood as association of the clusters with two-dimensional surfaces, whose area scales.Comment: 9 pages, 11 figure

    Probing Physics at Short Distances with Supersymmetry

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    We discuss the prospect of studying physics at short distances, such as Planck length or GUT scale, using supersymmetry as a probe. Supersymmetry breaking parameters contain information on all physics below the scale where they are induced. We will gain insights into grand unification (or in some cases string theory) and its symmetry breaking pattern combining measurements of gauge coupling constants, gaugino masses and scalar masses. Once the superparticle masses are known, it removes the main uncertainty in the analysis of proton decay, flavor violation and electric dipole moments. We will be able to discuss the consequence of flavor physics at short distances quantitatively.Comment: 20 pages, uses sprocl.sty, psfig.sty, to appear in `Perspectives on Supersymmetry', World Scientific, Editor G. Kan

    QCD at large and short distances (annotated version)

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    The formulation of QCD which contains no divergences and no renormalization procedure is presented. It contains both perturbative and non-perturbative phenomena. It is shown that, due to its asymptotically free nature, the theory is not defined uniquely. The chiral symmetry breaking and the nature of the octet of pseudo-scalar particles as quasi-Goldstone states are analysed in the theory with massless and massive quarks. The U(1) problem is discussed. ======================================================================= Note: The original version of the paper completed by the author in April 1997 was submitted to the hep-ph archive (hep-ph/9708424) a few days after Prof. V.N. Gribov passed away on August 13, 1997. This is the first of the two papers concluding his 20 year long study of the problem of quark confinement in QCD. In an attempt to understand the paper by a group of his colleagues, started in November 1997 in Orsay, this annotated version appeared. A number of misprints were eliminated, most of the equations were checked, and some corrected. Comments have been added in order to make the text easier to read. These comments are displayed in square brackets. Many theorists participated in the process; the comments were assembled and the final version prepared by Yu. Dokshitzer, C. Ewerz, A. Kaidalov, A. Mueller, J. Nyiri and A. Vainshtein. The second paper ``The theory of quark confinement'' will soon be published.Comment: 38 pages, Latex, 108 figures included using epsfig.sty. Annotated version of hep-ph/9708424, misprints eliminated, equations checked and some corrected, comments added (see abstract for further details