Velocity dependence of the nucleon-nucleon interaction,exchange currents and enhancement of the dipole sum rule in nuclei |
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Authors: | G.E. Brown Mannque Rho |
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Affiliation: | Physics Department, State University of New York at Stony Brook, Long Island, New York 11794 USA |
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Abstract: | A model is employed to describe the velocity dependence of the effective nucleon-nucleon interaction in nuclear matter. The interactions in this model consist of π? and ρ-meson exchange, together with short-range correlations induced by the strongly repulsive potential resulting from ω-meson exchange. With known coupling strengths, these interactions produce an effective mass in nuclear matter.Through the formalism of Fermi liquid theory, the exchange-current correction to the orbital g-factor, δgl, can be described in terms of the velocity dependence in the neutron-proton interaction, and, within the model, this can be related to the effective mass . With , the δgl for the proton turns out to be 0.22, 45% of it coming from π-meson exchange.Additional contributions to in nuclei come from the coupling of vibrations to quasiparticles; these are especially important in the nuclear surface, and tend to increase the effective mass, when averaged over both nuclear volume and surface, so that . In so far as these contributions arise from isovector vibrations, we can use the same model as for π- and ρ-meson exchange, and show that the same relation between and δgl holds, so that for , δgl = 0. The contributions from coupling to vibrations will depend upon the single-particle state, however; states of high-angular momentum will tend to have and δgl > 0.Finally, the enchancement δgl in gl can be connected with the enhancement k in the dipole sum rule originating from the giant-resonance region. This connection is not very precise, but gives a small positive κ ~ 0.2. |
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Keywords: | Nuclear reactions |
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