3,623 research outputs found

    ESC NN-Potentials in Momentum Space. II. Meson-Pair Exchange Potentials

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    The partial wave projection of the Nijmegen soft-core potential model for Meson-Pair-Exchange (MPE) for NN-scattering in momentum space is presented. Here, nucleon-nucleon momentum space MPE-potentials are NN-interactions where either one or both nucleons contains a meson-pair vertex. Dynamically, the meson-pair vertices can be viewed as describing in an effective way (part of) the effects of heavy-meson exchange and meson-nucleon resonances. From the point of view of ``duality,'' these two kinds of contribution are roughly equivalent. Part of the MPE-vertices can be found in the chiral-invariant phenomenological Lagrangians that have a basis in spontaneous broken chiral symmetry. It is shown that the MPE-interactions are a very important component of the nuclear force, which indeed enables a very succesful description of the low and medium energy NN-data. Here we present a precise fit to the NN-data with the extended-soft-core (ESC) model containing OBE-, PS-PS-, and MPE-potentials. An excellent description of the NN-data for TLab350T_{Lab} \leq 350 MeV is presented and discussed. Phase shifts are given and a χp.d.p.2=1.15\chi^2_{p.d.p.} = 1.15 is reached.Comment: 27 pages, 5 PostScript figures, revtex

    ESC NN-Potentials in Momentum Space. I. PS-PS Exchange Potentials

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    A momentum space representation is derived for the Nijmegen Extended-Soft-Core (ESC) interactions. The partial wave projection of this representation is carried through, in principle for Two-Meson-Exchange (TME) in general. Explicit results for the momentum space partial wave NN-potentials from PS-PS-Exchange are given.Comment: 23 pages, 2 PostScript figures, revtex

    Heavy flavour mass corrections to the longitudinal and transverse cross sections in e^+e^- - collisions

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    The sentence, 7th line below Eq. (28), starting with "Further we exclude all interference terms ...." is wrong and has been corrected. Eq. (33) : f_k^{l,(i)} -> h_k^{l,(i)} i=0,1 Second line below Eq. (33) m_bar(m)=m is replaced by m_bar(\mu_0)=\mu_0 with \mu_0=4.10 GeV and \mu_0=166.1 GeV for bottom and top respectively. The numbers in the third column of tables 1 and 2 are a little bit changed.Comment: 8 pages Latex, all compressed by uufile

    Soft-core baryon-baryon potentials for the complete baryon octet

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    SU(3) symmetry relations on the recently constructed hyperon-nucleon potentials are used to develop potential models for all possible baryon-baryon interaction channels. The main focus is on the interaction channels with total strangeness S=-2, -3, and -4, for which no experimental data exist yet. The potential models for these channels are based on SU(3) extensions of potential models for the S=0 and S=-1 sectors, which are fitted to experimental data. Although the SU(3) symmetry is not taken to be exact, the S=0 and S=-1 sectors still provide the necessary constraints to fix all free parameters. The potentials for the S=-2, -3, and -4 sectors, therefore, do not contain any additional free parameters, which makes them the first models of this kind. Various properties of the potentials are illustrated by giving results for scattering lengths, bound states, and total cross sections.Comment: 22 pages RevTex, 6 postscript figure

    Fully double-logarithm-resummed cross sections

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    We calculate the complete double logarithmic contribution to cross sections for semi-inclusive hadron production in the modified minimal-subtraction scheme by applying dimensional regularization to the double logarithm approximation. The full double logarithmic contribution to the coefficient functions for inclusive hadron production in electron-positron annihilation is obtained in this scheme for the first time. Our result agrees with all fixed order results in the literature, which extend to next-next-to-leading order.Comment: To appear in Nuclear Physics

    Couples’ decisions on having a first child

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    We investigate the decision-making process of having a first child, using theories on individualisation, lifestyle choices and negotiating partnerships as a starting point. We compare couples who had their first child at a relatively young age with those who had their first child at an older than average age, using data from semi-structured interviews with 33 couples, selected from the Netherlands Kinship Panel Study (NKPS). Although expecting more explicit decision-making among older parents, our qualitative analyses show that decision-making preceding both early and postponed first childbirth is often implicit. Disagreement between partners does not necessarily lead to discussion. Factors that result in the postponement of childbearing, such as higher education, do not always play a conscious role in people’s decision-making processes.couple decision-making, early parenthood, first birth, Netherlands, postponement of family formation, qualitative analysis

    Pion-Nucleon Scattering in Kadyshevsky Formalism: II Baryon Exchange Sector

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    In this paper, which is the second part in a series of two, we construct tree level baryon exchange and resonance amplitudes for πN\pi N / MBMB-scattering in the framework of the Kadyshevsky formalism. We use this formalism to formally implement absolute pair suppression, where we make use of the method of Takahashi and Umezawa. The resulting amplitudes are Lorentz invariant and causal. We continue studying the frame dependence of the Kadyshevsky integral equation using the method of Gross and Jackiw. The invariant amplitudes, including those for meson exchange, are linked to the phase-shifts using the partial wave basis.Comment: 49 page

    The geometry of whips

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    In this paper we study geometric aspects of the space of arcs parametrized by unit speed in the L2L^2 metric. Physically this corresponds to the motion of a whip, and it also arises in studying shape recognition. The geodesic equation is the nonlinear, nonlocal wave equation ηtt=s(σηs)\eta_{tt} = \partial_s(\sigma \eta_s), with ηs1\lvert \eta_s\rvert\equiv 1 and σ\sigma given by σssηss2σ=ηst2\sigma_{ss}- \lvert \eta_{ss}\rvert^2 \sigma = -\lvert \eta_{st}\rvert^2, with boundary conditions σ(t,1)=σ(t,1)=0\sigma(t,1)=\sigma(t,-1)=0 and η(t,0)=0\eta(t,0)=0. We prove that the space of arcs is a submanifold of the space of all curves, that the orthogonal projection exists but is not smooth, and as a consequence we get a Riemannian exponential map that it continuous and even differentiable but not C1C^1. This is related to the fact that the curvature is positive but unbounded above, so that there are conjugate points at arbitrarily short times along any geodesic. We also compare this metric to an L2L^2 metric introduced by Michor and Mumford for shape recognition on the homogeneous space Imm(I,R2)/D(I)\text{Imm}(I, \mathbb{R}^2)/\mathcal{D}(I) of immersed curves modulo reparametrizations; we show it has some similar properties (such as nonnegative but unbounded curvature and a nonsmooth exponential map), but that the L2L^2 metric on the arc space yields a genuine Riemannian distance.Comment: 24 page
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