New Developments of the Superradiant Nuclear Modell (original) (raw)
Related papers
Nuclear models and the hypernuclear interaction
1993
We present a first calculation of the potential and spin-orbit coupling for hypernuclei in the framework of a nuclear-potential model based on a spontaneous collective (superradiant) pion-nucleon-delta interaction. A perturbative evaluation of the propagation of a hyperon in such a coherent medium leads to an effective hypernuclear potential of the same shape and roughly half the depth (i.e. ~ 30 MeV) of the standard nuclear potential and a negligible spin-orbit coupling for both h and Z hypernuclei. Such results are in complete agreement with existing experimental data. Moreover, in this framework, we are able to explain the surprisingly narrow decay widths of the Z hypernuclei.
Resonance states below the pion-nucleon threshold and their consequences for nuclear systems
Physical Review C, 2003
Regular sequences of narrow peaks have been observed in the missing mass spectra in the reactions pp →p ϩ X and pd→ppX 1 below the pion-production threshold. They are interpreted in the literature as manifestations of supernarrow light dibaryons, nucleon resonances, or light pions forming resonance states with the nucleon in its ground state. We discuss how the existence of such exotic states would affect the properties of nuclear systems. We show that the neutron star structure is drastically changed in all three cases. We find that in the presence of dibaryons or nucleon resonances the maximal possible mass of a neutron star would be smaller than the observational limit. The presence of light pions does not contradict the observed neutron star masses. Light pions allow for the existence of extended nuclear objects of arbitrary size, bound by strong and electromagnetic forces.
A new approach to physics of nuclei
Physics of Atomic Nuclei, 2012
We employ the QCD sum rules method for description of nucleons in nuclear matter. We show that this approach provides a consistent formalism for solving various problems of nuclear physics. Such nucleon characteristics as the Dirac effective mass m * and the vector self-energy Σ V are expressed in terms of the in-medium values of QCD condensates. The values of these parameters at saturation density and the dependence on the baryon density and on the neutron-to-proton density ratio is in agreement with the results, obtained by conventional nuclear physics method. The contributions to m * and Σ V are related to observables and do not require phenomenological parameters. The scalar interaction is shown to be determined by the pion-nucleon σ-term. The nonlinear behavior of the scalar condensate may appear to provide a possible mechanism of the saturation. The approach provided reasonable results for renormalization of the axial coupling constant, for the contribution of the strong interactions to the neutron-proton mass difference and for the behavior of the structure functions of the in-medium nucleon. The approach enables to solve the problems which are difficult or unaccessible for conventional nuclear physics methods. The method provides guide-lines for building the nuclear forces. The threebody interactions emerge within the method in a natural way. There rigorous calculation will be possible in framework of self-consistent calculation in nuclear matter of the scalar condensate and of the nucleon effective mass m * .
Nuclear interactions in few-body systems
Czechoslovak Journal of Physics, 1989
Topics of nuclear interactions and meson-exchange currents in few-body systems are reviewed. The status of the effective nuclear theory is briefly examined and the impact of current research on the resolution ofopen problems is discussed. I. INTRODUCTION Recent theoretical nuclear investigations with few-body systems can be grouped into three categories. First, those which aim to render more complete the traditional effective theory of the nuclear medium based on non-relativistic meson-exchange phenomena with elementary nucleons and mesons. Second, those which attempt to take into accourir the compound nature of nucleons and mesons by means of microscopic QCD-inspired models for the structure and the interactions among these particles. Finally, those which look at novel testing grounds for nuclear theoretical ideas, anticipating the advent of new experimental facilities and proposing novel experimental tests. The first category includes, among other things, the continuing effort to improve the boson-exchange models (OBE) of the NN interaction, the introduction of relativistic aspects in the two-nucleon and multi-nucleon theory, and the incorporation of meson-exchange currents (MEC) in all photoreactions and weak interaction processes. The second group of investigations spans the work on constituent quark models, bag and solution models of nucleons and mesons, and the search for convincing signais of such structures in short-range correlations in nuclear systems and in electroand photo-reactions. Prominent among the investigations in the third category is research into spin observables in scattering of polarized projectiles from polarized or unpolarized targets, analysis of data from double and triple coincidence experiments, leading to enhanced sensitivity to the underlying dynamics, systematic experimental studies of excited baryons, and searches for dibaryons. lin the following, we will summarize the current status of relevant theoretical constructs in these areas of research related to the work that was contributed to this conference, and we will review these contributions to discover how they help to resolve open problems in nuclear physics.
Pauli principle and renormalization of the pion nucleon interaction in nuclei
Physics Letters B, 1976
We show that the exclusion principle provides an alternative mechanism to the Lorentz-Lorenz effect for the renormalization of the pion-nucleon coupling constant in nuclei. This mechanism proves to be less sensitive to the range of the ~r -N forces. The implications for pion-nucleus scattering are discussed.
Relevance of high-momentum nucleons for nuclear phenomena
2001
A brief review is given concerning the status of the theoretical work on nucleon spectral functions. A recent concern about the validity of the concept of spectroscopic factors as deduced from (e,e ′ p) reactions at higher Q 2 , is discussed in some detail. The consequences of the observed spectral strength are then considered in the context of nuclear saturation. It is argued that short-range correlations are mainly responsible for the actual value of the observed charge density in 208 Pb and by extension for the empirical value of the saturation density of nuclear matter. This observation combined with the general understanding of the spectroscopic strength suggests that a renewed study of nuclear matter, emphasizing the selfconsistent determination of the spectral strength due to short-range and tensor correlations, may shed light on the perennial nuclear saturation problem. First results using such a scheme are presented.
Nuclear Structure Studies with Realistic Nucleon-Nucleon Forces
Studies on the structure of nuclear systems are performed, ~which are based on realistic nucleon-nucleon interactions. Such realistic interactions induce two-body correlations in the nuclear many-body wave function. In particular one finds deviations of the single-particle Green's function from the mean field prediction of a Hartree-Fock theory. Such modifications give rise to a modification in the response function of the nuclear system. This response function characterizes the excitation modes of the nuclear system. It is also the most relevant ingredient for the study of the propagator of a meson in the nuclear medium. This meson propagators, on the other hand, ~are very important to study modifications of the nucleon-nucleon force in the nuclear medium and thereby influence the self-consistent evaluation of the single-particle Green's function. The nuclear spectral function at high missing energies and momenta has been determined from a self-consistent calculation of the...
The interaction in nuclear matter from a study of the reactions
Nuclear Physics A, 2000
The pion-production reactions π + A → π + π ± A ′ were studied on 2 H, 12 C, 40 Ca, and 208 P b nuclei at an incident pion energy of T π + =283 MeV. Pions were detected in coincidence using the CHAOS spectrometer. The experimental results are reduced to differential cross sections and compared to both theoretical predictions and the reaction phase space. The composite ratio C A ππ between the π + π ± invariant masses on nuclei and on the nucleon is also presented. Near the 2m π threshold pion pairs couple to (ππ) I=J=0 when produced in the π + → π + π − reaction channel. There is a marked near-threshold enhancement of C A π + π − which is consistent with theoretical predictions addressing the partial restoration of chiral symmetry in nuclear matter. Furthermore, the behaviour of C A π + π − is well described when the restoration of chiral symmetry is combined with standard Pwave renormalization of pions in nuclear matter. On the other hand, nuclear matter only weakly influences C A π + π + , which displays a flat behaviour throughout the energy range regardless of A.
1.1 General survey It is customary to regard nuclear physics as the field of study that includes the structure of atomic nuclei, the reactions that take place between them, and the techniques, both experimental and theoretical, that shed light on these subjects. Rigid adherence to such limits would, however, exclude much that is both exciting and informative. The nucleus entered physics as a necessary component of the atomic model and nuclear effects in spectroscopy and solid state physics now provide not only elegant methods for determination of nuclear properties but also convincing demonstrations of the powers of quantum mechanics. Equally, those particles sometimes described as elementary or fundamental, although first recognized in the cosmic radiation, soon assumed a role of importance in nuclear problems, especially in the understanding of the forces between neutrons and protons. Advances in the study of particles, or sub-nuclear physics, besides leading to the discovery of new and previously unsuspected physical laws, have frequently stimulated back-reference to complex nuclei