6,918 research outputs found

    High-precision covariant one-boson-exchange potentials for np scattering below 350 MeV

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    All realistic potential models for the two-nucleon interaction are to some extent based on boson exchange. However, in order to achieve an essentially perfect fit to the scattering data, characterized by a chi2/Ndata ~ 1, previous potentials have abandoned a pure one boson-exchange mechanism (OBE). Using a covariant theory, we have found a OBE potential that fits the 2006 world np data below 350 MeV with a chi2/Ndata = 1.06 for 3788 data. Our potential has fewer adjustable parameters than previous high-precision potentials, and also reproduces the experimental triton binding energy without introducing additional irreducible three-nucleon forces.Comment: 4 pages; revised version with augmented data sets; agrees with published versio

    The shape of the Δ\Delta baryon in a covariant spectator quark model

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    Using a covariant spectator quark model that describes the recent lattice QCD data for the Δ\Delta electromagnetic form factors and all available experimental data on γN→Δ\gamma N \to \Delta transitions, we analyze the charge and magnetic dipole distributions of the Δ\Delta baryon and discuss its shape. We conclude that the quadrupole moment of the Δ\Delta is a good indicator of the deformation and that the Δ+\Delta^+ charge distribution has an oblate shape. We also calculate transverse moments and find that they do not lead to unambiguous conclusions about the underlying shape.Comment: Extended introduction, references added, other small modifications. To appear in Phys. Rev. D. 14 pages, 8 figure

    Dynamical diversity and metastability in a hindered granular column near jamming

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    Granular media jam into a panoply of metastable states. The way in which these states are achieved depends on the nature of local and global constraints on grains; here we investigate this issue by means of a non-equilibrium stochastic model of a hindered granular column near its jamming limit. Grains feel the constraints of grains above and below them differently, depending on their position. A rich phase diagram with four dynamical phases (ballistic, activated, logarithmic and glassy) is revealed. The statistics of the jamming time and of the metastable states reached as attractors of the zero-temperature dynamics is investigated in each of these phases. Of particular interest is the glassy phase, where intermittency and a strong deviation from Edwards' flatness are manifest.Comment: 23 pages, 12 figure

    Comment on ``Relativistic cluster dynamics of nucleons and mesons. II. Formalism and examples''

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    In a recent paper [Phys.\ Rev.\ C{\bf 49}, 2142 (1994)], Haberzettl presented cluster N-body equations for arbitrarily large systems of nucleons and mesons. Application to the three-nucleon system is claimed to yield a new kind of three-nucleon force. We demonstrate that these three-nucleon equations contain double counting.Comment: 6 pages in Revtex 3.0, 6 Postscript figures. Accepted for publication in Phys. Rev.
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