Covariant representations of the relativistic Brueckner T-matrix and the nuclear matter problem

Abstract

We investigate nuclear matter properties in the relativistic Brueckner approach. The in-medium on-shell T-matrix is represented covariantly by five Lorentz invariant amplitudes from which we deduce directly the nucleon self-energy. We discuss the ambiguities of this approach and the failure of previously used covariant representations in reproducing the nucleon self-energies on the Hartree-Fock level. To enforce correct Hartree-Fock results we develop a subtraction scheme which treats the bare nucleon-nucleon potential exactly in accordance to the different types of meson exchanges. For the remaining ladder kernel, which contains the higher order correlations, we employ then two different covariant representations in order to study the uncertainty inherent in the approach. The nuclear matter bulk properties are only slightly sensitive on the explicit representation used for the kernel. However, we obtain new Coester lines for the various Bonn potentials which are shifted towards the empirical region of saturation. In addition the nuclear equation-of-state turns out to be significantly softer in the new approach.

Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes

“…A possibility would be to perform a Taylor expansion of the self-energy components in terms of the momentum [24]. Since the intrinsic momentum dependence of the DBHF self-energy components is generally weak [16,18] we neglect such additional correction terms. The new renormalized isoscalar density dependent coupling functions are reduced by an amount of 15-20 MeV compared to the corresponding nonrenormalized coupling functions in fig.…”

Relativistic nuclear model with point-couplings constrained by QCD and chiral symmetry

“…In order to determine the density dependence of the couplings from Eqs. (35) - (38), the CHPT self-energies are re-expressed in terms of the baryon density ρ = 2k 3 f /3π 2 :…”

“…We refer here explicitly to a calculation, reported in Ref. [38], which uses the Bonn A potential. With this potential, the nuclear matter saturation density comes out somewhat higher (ρ sat ≃ 0.185 fm −3 ) than the one of our best fit.…”

Neutron star structure from a quark-model baryon-baryon interaction

“…In those cases the Argonne v 18 NN potential is used along with the Urbana model for 3N forces [9]. The other curves show results obtained with BHF and microscopic 3N forces [10], and the relativistic DBHF [11]. We observe that the fss2 EOS is quite soft at high densities, and that all EOS agree well in symmetric matter up to nucleonic density ρ ∼ 0.5 fm −3 .…”