1,721,251 research outputs found
Chiral pion–nucleon dynamics in finite nuclei: Spin–isospin excitations
No full textThe nuclear density functional framework, based on chiral dynamics and the symmetry breaking pattern of low-energy QCD, is extended to the description of collective nuclear excitations. Starting from the relativistic point-coupling Lagrangian introduced in [P. Finelli, N. Kaiser, D. Vretenar, W. Weise, Nucl. Phys. A 770 (2006) 1], the proton–neutron (quasiparticle) random phase approximation is formulated and applied to investigate the role of chiral pion–nucleon dynamics in excitation modes involving spin and isospin degrees of freedom, e.g. isobaric analog states and Gamow–Teller resonances
The pi-nucleus optical potential to O(p(5)) in Chiral Perturbation Theory
No full textWe describe the calculation of the pi-nucleus optical potential to NLO in Chiral Perturbation Theory (ChPT) within a new formulation of the effective theory in the presence of a nuclear background, characterized by a static, non-uniform distribution of the baryon number, describing the finite nucleus. This formulation reduces to the conventional In-medium ChPT in the case of a uniform distribution. In this way we are able to identify unambiguously the nuclear finite size effects and disentangle the S-, P- and D-wave contributions to the optical potential without invoking the local density approximation
Chiral perturbation theory in a nuclear background
No full textWe propose a novel way to formulate chiral perturbation theory (ChPT) in a nuclear background, characterized by a static, non-uniform distribution of the baryon number that describes the finite nucleus. In the limiting case of a uniform distribution, the theory reduces to the well-known zero-temperature in-medium ChPT. The proposed approach is used to calculate the self-energy of the charged pion in the background of the heavy nucleus at O(p(5)) in the chiral expansion, and to derive the leading terms of the pion-nucleus optical potential
Relativistic nuclear energy density functional constrained by low-energy QCD
No full textA relativistic nuclear energy density functional is developed, guided by two important features that establish connections with chiral dynamics and the symmetry breaking pattern of low-energy QCD: (a) strong scalar and vector fields related to in-medium changes of QCD vacuum condensates; (b) the long- and intermediate-range interactions generated by one- and two-pion exchange, derived from in-medium chiral perturbation theory, with explicit inclusion of Δ(1232) excitations. Applications are presented for binding energies, radii of proton and neutron distributions and other observables over a wide range of spherical and deformed nuclei from 16O to 210Po. Isotopic chains of Sn and Pb nuclei are studied as test cases for the isospin dependence of the underlying interactions. The results are at the same level of quantitative comparison with data as the best phenomenological relativistic mean-field models
Nuclear density functional constrained by low-energy QCD
No full textWe have developed a relativistic point-coupling model of nuclear many-body dynamics constrained by the low-energy sector of QCD. The effective Lagrangian is characterized by density-dependent coupling strengths determined by chiral one- and two-pion exchange (with single and double delta isobar excitations) and by large isoscalar background fields that arise through changes of the quark condensate and the quark density at finite baryon density. The model has been tested in the analysis of nuclear ground-state properties along different isotope chains of medium and heavy nuclei. The agreement with experimental data is comparable with purely phenomenological predictions. The built-in QCD constraints and the explicit treatment of pion exchange restrict the freedom in adjusting parameters and functional forms of density-dependent couplings. It is shown that chiral pionic fluctuations play an important role for nuclear binding and saturation mechanism, whereas background fields of about equal magnitude and opposite sign generate the effective spin-orbit potential in nuclei
In-medium chiral SU(3) dynamics and hypernuclear structure
No full textA previously introduced relativistic energy density functional, successfully applied to ordinary nuclei, is extended to hypernuclei. The density-dependent mean field and the spin–orbit potential are consistently calculated for a Λ hyperon in the nucleus using the SU(3) extension of in-medium chiral perturbation theory. The leading long range ΛN interaction arises from kaon-exchange and 2π-exchange with Σ hyperon in the intermediate state. Scalar and vector mean fields reflecting in-medium changes of the quark condensates are constrained by QCD sum rules. The model, applied to oxygen as a test case, describes spectroscopic data in good agreement with experiment. In particular, the smallness of the Λ spin–orbit interaction finds a natural explanation in terms of an almost complete cancellation between scalar–vector background contributions and long-range terms generated by two-pion exchange
Relativistic nuclear model with point couplings constrained by QCD and chiral symmetry
No full textWe derive a microscopic relativistic point-coupling model of nuclear many-body dynamics constrained by in-medium QCD sum rules and chiral symmetry. The effective Lagrangian is characterized by density dependent coupling strengths, determined by chiral one- and two-pion exchange and by QCD sum rule constraints for the large isoscalar nucleon self-energies that arise through changes of the quark condensate and the quark density at finite baryon density. This approach is tested in the analysis of the equations of state for symmetric and asymmetric nuclear matter, and of bulk and single-nucleon properties of finite nuclei. In comparison with purely phenomenological mean-field approaches, the built-in QCD constraints and the explicit treatment of pion exchange restrict the freedom in adjusting parameters and functional forms of density dependent couplings. It is shown that chiral (two-pion exchange) fluctuations play a prominent role for nuclear binding and saturation, whereas strong scalar and vector fields of about equal magnitude and opposite sign, induced by changes of the QCD vacuum in the presence of baryonic matter, generate the large effective spin-orbit potential in finite nuclei
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