dorsal/arxiv
View SchemaCausality in relativistic many body theory
| Authors | H. Blum, R. Brockmann |
|---|---|
| Categories | |
| ArXiv ID | nucl-th/9902003 |
| URL | https://arxiv.org/abs/nucl-th/9902003 |
| DOI | 10.1103/PhysRevC.59.2546 |
| Journal | Phys.Rev. C59 (1999) 2546-2557 |
Abstract
The stability of the nuclear matter system with respect to density fluctuations is examined exploring in detail the pole structure of the electro-nuclear response functions. Making extensive use of the method of dispersion integrals we calculate the full polarization propagator not only for real energies in the spacelike and timelike regime but also in the whole complex energy plane. The latter proved to be necessary in order to identify unphysical causality violating poles which are the consequence of a neglection of vacuum polarization. On the contrary it is shown that Dirac sea effects stabilize the nuclear matter system shifting the unphysical pole from the upper energy plane back to the real axis. The exchange of strength between these real timelike collective excitations and the spacelike energy regime is shown to lead to a reduction of the quasielastic peak as it is seen in electron scattering experiments. Neglecting vacuum polarization one also obtains a reduction of the quasielastic peak but in this case the strength is partly shifted to the causality violating pole mentioned above which consequently cannot be considered as a physical reliable result. Our investigation of the response function in the energy region above the threshold of nucleon anti-nucleon production leads to another remarkable result. Treating the nucleons as point-like Dirac particles we show that for any isospin independent NN-interaction RPA-correlations provide a reduction of the production amplitude for $p\bar p$-pairs by a factor 2.
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"abstract": "The stability of the nuclear matter system with respect to density\nfluctuations is examined exploring in detail the pole structure of the\nelectro-nuclear response functions. Making extensive use of the method of\ndispersion integrals we calculate the full polarization propagator not only for\nreal energies in the spacelike and timelike regime but also in the whole\ncomplex energy plane. The latter proved to be necessary in order to identify\nunphysical causality violating poles which are the consequence of a neglection\nof vacuum polarization. On the contrary it is shown that Dirac sea effects\nstabilize the nuclear matter system shifting the unphysical pole from the upper\nenergy plane back to the real axis. The exchange of strength between these real\ntimelike collective excitations and the spacelike energy regime is shown to\nlead to a reduction of the quasielastic peak as it is seen in electron\nscattering experiments. Neglecting vacuum polarization one also obtains a\nreduction of the quasielastic peak but in this case the strength is partly\nshifted to the causality violating pole mentioned above which consequently\ncannot be considered as a physical reliable result. Our investigation of the\nresponse function in the energy region above the threshold of nucleon\nanti-nucleon production leads to another remarkable result. Treating the\nnucleons as point-like Dirac particles we show that for any isospin independent\nNN-interaction RPA-correlations provide a reduction of the production amplitude\nfor $p\\bar p$-pairs by a factor 2.",
"arxiv_id": "nucl-th/9902003",
"authors": [
"H. Blum",
"R. Brockmann"
],
"categories": [
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"doi": "10.1103/PhysRevC.59.2546",
"journal_ref": "Phys.Rev. C59 (1999) 2546-2557",
"title": "Causality in relativistic many body theory",
"url": "https://arxiv.org/abs/nucl-th/9902003"
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