Fock exchange terms in nonlinear quantum hadrodynamics

The Equation of State (EOS) for asymmetric nuclear matter is discussed starting from a phenomenological hadronic field theory of Serot-Walecka type including exchange terms. In a model with self interactions of the scalar sigma-meson we show that the Fock terms naturally lead to isospin effects in the nuclear EOS. These effects are quite large and dominate over the contribution due to isovector mesons. We obtain a potential symmetry term of "stiff" type, i.e. increasing with baryon density and an interesting behaviour of neutron/proton effective masses of relevance for transport properties of asymmetric dense matter.Phenomenological hadronic field theories (Quantum Hadrodynamics, QHD) are widely used in dense nuclear matter studies since relativistic effects are expected to increase with baryon density [1]. In most of the previous works on the subject, the Relativistic Mean Field (RMF ) approximation of QHD has been followed. In the RMF the meson fields are treated as classical fields and consequently a Hartree reduction of one body density matrices is used.Although the model has driven a large amount of results on relativistic effects in nuclear structure and dynamics [2-6], the lack of exchange terms has implied some non satisfying features of the theory and some efforts have been done to try to cure this problem [7][8][9][10]. In the RMF theory each meson field is introduced, with appropriated readjusted couplings, just to describe the dynamics of a corresponding degree of freedom, without mixing due to many-body effects. Neutral σ and ω mesons are in charge of saturation properties, isospin effects are carried by isovector δ [a 0 (980)] and ρ mesons and finally spin terms are coming from pseudoscalar π and η fields. In a sense the model represents a straightforward extension of the One-Boson-Exchange (OBE) description of nucleon-nucleon scattering.The aim of this letter is to introduce explicit many-body effects just evaluating exchange term contributions. We will get qualitative new features of equilibrium (EOS) and dynamical properties of asymmetric nuclear matter. In particular a new density dependence of the symmetry term is expected, at variance with the simple linear increase predicted by the ρ−exchange mechanism in the Hartree scheme.

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“…[17]. We have verified that the used approximation leads to a thermodynamically consistent theory [16].…”

Section: Introductionmentioning

confidence: 79%

Asymmetric nuclear matter in a Hartree-Fock approach to nonlinear quantum hadrodynamics

et al. 2001

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“…In particular in our case the coupling functions to the scalar-isoscalar channel depend on all the isoscalar and isovector densities and currents (for details, see [24]), then it is even more general.…”

Section: Linear Response Equationsmentioning

confidence: 99%

“…Following the treatment of the Fock terms in non-linear QHD introduced in Ref. [24,25], we obtain for the Wigner function the following kinetic equation:…”

Section: Kinetic Equations From a Qhd Effective Theorymentioning

confidence: 99%

“…The energy density and pressure for symmetric and asymmetric nuclear matter and the n, p effective masses can be self-consistently calculated just in terms of the four boson coupling constants, f i ≡ ( [24,25]. The isoscalar meson parameters are fixed from symmetric nuclear matter properties at T = 0: saturation density ρ 0 = 0.16f m −3 , binding energy E/A = −16M eV , nucleon effective mass M ⋆ = 0.7M N (M N = 939M eV ) and incompressibility K V = 240M eV at ρ 0 .…”

Section: Equilibrium Properties: the Nuclear Equation Of Statementioning

confidence: 99%

“…We will discuss this point later. A thorough study of the Fock contributions in a QHD approach with non-linear self-interacting terms has been recently performed [24], in particular for asymmetric matter [25].…”

Section: Kinetic Equations From a Qhd Effective Theorymentioning

confidence: 99%

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Collective modes of asymmetric nuclear matter in quantum hadrodynamics

et al. 2003

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We discuss a fully relativistic Landau Fermi liquid theory based on the Quantum HadroDynamics (QHD) effective field picture of Nuclear Matter (NM). From the linearized kinetic equations we get the dispersion relations of the propagating collective modes. We focus our attention on the dynamical effects of the interplay between scalar and vector channel contributions. A beautiful "mirror" structure in the form of the dynamical response in the isoscalar/isovector degree of freedom is revealed, with a complete parallelism in the role respectively played by the compressibility and the symmetry energy. All that strongly supports the introduction of an explicit coupling to the scalar-isovector channel of the nucleon-nucleon interaction.In particular we study the influence of this coupling (to a δ-meson-like effective field) on the collective response of asymmetric nuclear matter (AN M ). Interesting contributions are found on the propagation of isovector-like modes at normal density and on an expected smooth transition to isoscalar-like oscillations at high baryon density.Important "chemical" effects on the neutron-proton structure of the mode are shown. For dilute AN M we have the isospin distillation mechanism of the unstable isoscalar-like oscillations, while at high baryon density we predict an almost pure neutron wave structure of the propagating sounds.

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Fluctuations and Instabilities in Nuclear Dynamics: from Multifragmentation to Neutron Stars

Toro¹

2004

Nonequilibrium Physics at Short Time Scales

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Fock exchange terms in nonlinear quantum hadrodynamics

Cited by 19 publications

References 27 publications

Asymmetric nuclear matter in a Hartree-Fock approach to nonlinear quantum hadrodynamics

Asymmetric nuclear matter in a Hartree-Fock approach to nonlinear quantum hadrodynamics

Collective modes of asymmetric nuclear matter in quantum hadrodynamics

Fluctuations and Instabilities in Nuclear Dynamics: from Multifragmentation to Neutron Stars

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