Interaction In Nuclear Matter Research Articles

Quasiparticle interaction in nuclear matter with chiral three-nucleon forces

We derive the effective interaction between two quasiparticles in symmetric nuclear matter resulting from the leading-order chiral three-nucleon force. We restrict our study to the L=0,1 Landau parameters of the central quasiparticle interaction computed to first order. We find that the three-nucleon force provides substantial repulsion in the isotropic spin- and isospin-independent component F_0 of the interaction. This repulsion acts to stabilize nuclear matter against isoscalar density oscillations, a feature which is absent in calculations employing low-momentum two-nucleon interactions only. We find a rather large uncertainty for the nuclear compression modulus due to a sensitive dependence on the low-energy constant c_3. The effective nucleon mass on the Fermi surface, as well as the nuclear symmetry energy, receive only small corrections from the leading-order chiral three-body force. Both the anomalous orbital g-factor and the Landau-Migdal parameter g'_{NN} (characterizing the spin-isospin response of nuclear matter) decrease with the addition of three-nucleon correlations. In fact, the anomalous orbital g-factor remains significantly smaller than its value extracted from experimental data, whereas g'_{NN} still compares well with empirical values. The inclusion of the three-nucleon force results in relatively small p-wave (L=1) components of the central quasiparticle interaction, thus suggesting an effective interaction of short range.

Second-order quasiparticle interaction in nuclear matter with chiral two-nucleon interactions

We employ Landau's theory of normal Fermi liquids to study the quasiparticle interaction in nuclear matter in the vicinity of saturation density. Realistic low-momentum nucleon-nucleon interactions evolved from the Idaho N3LO chiral two-body potential are used as input potentials. We derive for the first time exact results for the central part of the quasiparticle interaction computed to second order in perturbation theory, from which we extract the L=0 and L=1 Landau parameters as well as some relevant bulk equilibrium properties of nuclear matter. The accuracy of the intricate numerical calculations is tested with analytical results derived for scalar-isoscalar boson exchange and (modified) pion exchange at second order. The explicit dependence of the Fermi liquid parameters on the low-momentum cutoff scale is studied, which provides important insight into the scale variation of phase-shift equivalent two-body potentials. This leads naturally to explore the role that three-nucleon forces must play in the effective interaction between two quasiparticles.

New type of Pairing interactions in nuclear matter and finite nuclei

We propose new types of density dependent contact pairing interaction which reproduce pairing gaps in a wide range of nuclear mass table.We discuss also the relation between the proposed paring interactions and the pairing gaps in symmetric and neutron matters obtained by a microscopic treatment based on a bare nucleon-nucleon interaction. It is shown that the isovector type pairing interaction is necessary on top of the isoscalar term to reproduce systematically nuclear empirical pairing gaps. The BCS-BEC crossover of neutrons pairs in symmetric and asymmetric nuclear matters is studied by using these contact interactions. It is shown that the bare and screened pairing interactions lead to different features of the BCS-BEC crossover in symmetric nuclear matter.

How deep is the antinucleon optical potential at FAIR energies

The key question in the interaction of antinucleons in the nuclear medium concerns the deepness of the antinucleon–nucleus optical potential. In this work we study this task in the framework of the non-linear derivative (NLD) model which describes consistently bulk properties of nuclear matter and Dirac phenomenology of nucleon–nucleus interactions. We apply the NLD model to antinucleon interactions in nuclear matter and find a strong decrease of the vector and scalar self-energies in energy and density and thus a strong suppression of the optical potential at zero momentum and, in particular, at FAIR energies. This is in agreement with available empirical information and, therefore, resolves the issue concerning the incompatibility of G-parity arguments in relativistic mean-field (RMF) models. We conclude the relevance of our results for the future activities at FAIR.

Static and Covariant Meson-Exchange Interactions in Nuclear Matter

The Dirac version of static meson exchange interactions provides a good description of low-energy NN scattering as well as very reasonable saturation properties in Dirac–Brueckner calculations of nuclear matter. We include retardation terms to make these interactions covariant and readjust the coupling constants so as to maintain a reasonable description of NN scattering. In this case, we find the Dirac–Brueckner approximation to nuclear matter to be extremely overbound.

Dirac-Brueckner mean fields and the effective Dirac-Hartree-Fock interaction in nuclear matter

Our objective is to include Fock exchange terms, and thus the pion, in a Dirac description of nuclear matter and to determine a density-dependent Dirac-Hartree-Fock meson exchange interaction that is hopefully less density-dependent than a typical Hartree one. We begin by performing extended self-consistent nuclear matter Dirac-Brueckner calculations over a wide range of densities and asymmetries. We maintain the momentum dependence of the Brueckner mean fields in the hope of fitting it with the momentum dependence of the effective Dirac-Hartree-Fock mean fields. To improve the description of the Brueckner mean fields within a Hartee-Fock approximation, we include contact terms in the interaction.

Constraining the nuclear pairing gap with pairing vibrations

Pairing interactions with various density dependencies (surface/volume mixing) are constrained with the two-neutron separation energy in the tin isotopic chain. The response associated with pairing vibrations in very neutron-rich nuclei is sensitive to the density dependence of the pairing interaction. Using the same pairing interaction in nuclear matter and in tin nuclei, the optimal range of densities relevant for the pairing channel is also studied.

A Separable Pairing Force in Nuclear Matter

The method introduced by Duguet is adopted to derive aseparable form of the pairing interaction in the 1S0 channel from a bare or aneffective nucleon–nucleon (NN) interaction in nuclear matter. With this approachthe separable pairing interaction reproduces the pairing properties provided by itscorresponding NN interaction. In this work, separable forms of pairing interactionsin the 1S0 channel for the bare NN interaction, Bonn potential and the Gognyeffective interaction are obtained. It is found that the separable force of theGogny effective interaction in the 1S0 channel has a clear link with the bare NNinteraction. With such a simple separable form pairing properties provided by theGogny force in nuclear matter can be reproduced.

Correlations and effective interactions in nuclear matter

We performed Self-Consistent Greens Function (SCGF) calculations for symmetric nuclear matter using realistic nucleon-nucleon (NN) interactions and effective low-momentum interactions ($V_{low-k}$), which are derived from such realistic NN interactions. We compare the spectral distributions resulting from such calculations. We also introduce a density-dependent effective low-momentum interaction which accounts for the dispersive effects in the single-particle propagator in the medium.

Quasi-particle interaction in nuclear matter from chiral pion–nucleon dynamics

Based on a recent chiral approach to nuclear matter we calculate the in-medium interaction of nucleons at the Fermi surface | p → 1 , 2 | = k f . The isotropic part of this quasi-particle interaction is characterized by four density-dependent (dimensionful) Fermi-liquid parameters: f 0 ( k f ) , f 0 ′ ( k f ) , g 0 ( k f ) and g 0 ′ ( k f ) . In the approximation to 1 π-exchange and iterated 1 π-exchange (which as such leads already to a good nuclear matter equation of state) we find a spin–isospin interaction strength of g 0 ′ ( 2 m π ) = 1.14 fm 2 , compatible with existing empirical values. The consistency relations to the nuclear matter compressibility K and the spin/isospin asymmetry energies serve as a check on our perturbative calculation. In the next step we include systematically the contributions from 2 π-exchange with virtual Δ ( 1232 ) -isobar excitation which have been found important for good single-particle properties and spin-stability of nuclear matter. Without any additional short-distance terms (contributing proportional to k f 2 ) the spin-dependent Fermi-liquid parameters g 0 ( k f 0 ) and g 0 ′ ( k f 0 ) come out far too large. Estimates of these short-distance parameters from realistic NN-potentials go in the right direction, but sizeable enhancement factors are still needed to reproduce the empirical values of g 0 ( k f 0 ) and g 0 ′ ( k f 0 ) . This points towards the importance of higher order iterations subsumed in the induced interaction. We consider also the tensor part of the quasi-nucleon interaction at the Fermi surface. In comparison to the leading 1 π-exchange tensor interaction we find from the 2 π-exchange corrections almost a doubling of the isoscalar tensor strength h 0 ( k f ) , whereas the isovector tensor strength h 0 ′ ( k f ) is much less affected. These features are not changed by the inclusion of the chiral πNΔ-dynamics. The l = 1 tensor Fermi-liquid parameters h 1 ( k f ) and h 1 ′ ( k f ) follow a similar pattern.

Effective Hadron Masses and Effective Interactions in Nuclear Matter

Relations among the effective hadron masses and the effective interactions in nuclear matter are studied by using the generalized relativistic mean field theory. We found that we can make the effective omega-meson mass smaller and the equation of state softer if we require that the omega-meson mean field is proportional to the baryon density. In this case, there is a simple and exact relation between the effective omega-meson mass and the effective omega-nucleon coupling. Because of this relation, the effective omega-nucleon coupling automatically decreases if the effective omega-meson mass decreases. Consequently, the equation of state becomes softer. A trial to embed the QCD sum-rule results into the hadron field theory is also shown.

Hybrid meson potentials and the gluonic van der Waals force

The chromoelectric polarizability of mesons governs the strength of the gluonic van der Waals force and therefore of non-quark-exchange processes in hadronic physics. We compute the polarizability of heavy mesons with the aid of lattice gauge theory and the Born–Oppenheimer adiabatic expansion. We find that the operator product expansion breaks down at surprisingly large quarks masses due to nonperturbative gluodynamics and that previous conclusions concerning J/ψ–nuclear matter interactions and J/ψ dissociation in the quark–gluon plasma must be substantially modified.

EFFECTIVE NUCLEON-NUCLEON INTERACTION AND FERMI LIQUID THEORY

We present two novel relations between the quasiparticle interaction in nuclear matter and the unique low momentum nucleon-nucleon interaction in vacuum. These relations provide two independent constraints on the Fermi liquid parameters of nuclear matter. Moreover, the new constraints define two combinations of Fermi liquid parameters, which are invariant under the renormalisation group flow in the particle-hole channels. Using empirical values for the spin-independent Fermi liquid parameters, we are able to compute the major spin-dependent ones by imposing the new constraints as well as the Pauli principle sum rules.

The structure of nuclear systems derived from low momentum nucleon–nucleon potentials

Various nuclear structure observables are evaluated employing low-momentum nucleon–nucleon (NN) potentials V low- k derived from the CD-Bonn and Nijmegen NN interactions V NN. By construction, the high momentum modes of the original V NN are integrated out in V low- k , with the requirement that the deuteron binding energy and low energy phase shifts of V NN are exactly reproduced. Using this interaction, we evaluate the bulk properties (binding energy and saturation density) of nuclear matter and finite nuclei, in particular their dependence on the cut-off parameter. We also study the pairing gap and the residual interaction in nuclear matter in terms of the Landau parametrization. At low and medium densities, the HF and BHF binding energies for nuclear matter calculated with the V low- k 's derived from the CD-Bonn and Nijmegen potentials are nearly identical. The pairing gaps and Landau parameters derived from V low- k are remarkably close to those given by the full-space V NN. The V low- k interactions, however, fail to reproduce the saturation property of nuclear matter at higher densities if the cut-off for the high momentum modes is assumed density independent.

$$\bar K$$ optical potential at finite temperatureoptical potential at finite temperature

The \(\bar K\) optical potential is microscopically calculated from the \(\bar K\)N effective interaction in nuclear matter at T=0 and finite temperature, with the aim to adapt our calculations to the experimental conditions in heavy-ion collisions. In the rank of densities (0-2ρ0), the finite temperature \(\bar K\) optical potential shows a smoother behaviour compared to the T=0 case. The model has also been applied to the study of the ratio between K+ and K− produced at GSI with T around 70 MeV. The results point at the necessity of introducing an attractive \(\bar K\) optical potential.

Low-momentum nucleon–nucleon interaction and Fermi liquid theory

We use the induced interaction of Babu and Brown to derive two novel relations between the quasiparticle interaction in nuclear matter and the unique low-momentum nucleon–nucleon interaction V low k in vacuum. These relations provide two independent constraints on the Fermi liquid parameters of nuclear matter. We derive the full renormalization group equations in the particle–hole channels from the induced interaction. The new constraints, together with the Pauli principle sum rules, define four combinations of Fermi liquid parameters that are invariant under the renormalization group flow. Using empirical values for the spin-independent Fermi liquid parameters, we are able to compute the major spin-dependent ones by imposing the new constraints and the Pauli principle sum rules. The effects of tensor forces are discussed.

Chiral unitary theory: Application to nuclear problems

In this talk we briefly describe some basic elements of chiral perturbation theory, $\chi PT$, and how the implementation of unitarity and other novel elements lead to a better expansion of the $T$ matrix for meson meson and meson baryon interactions. Applications are then done to the $ \pi \pi $ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and $K^-$ atoms, and how the $\phi$ meson properties are changed in a nuclear medium.

Suppression of charmonia in nuclear matter

We study the recent E866/NuSea charmonium data obtained at Fermilab. For the first time in hadron-nucleus collisions these show evidence for two distinct regimes in ψ′ vs J/ψ production. We confront this pattern with a simple scenario of cc̄ evolution and interaction in nuclear matter.

The [formula omitted] interaction in nuclear matter from a study of the [formula omitted] reactions

The pion-production reactions π+A→π+π±A′ were studied on 2H, 12C, 40Ca, and 208Pb nuclei at an incident pion energy of Tπ+=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 CππA between the π+π± invariant masses on nuclei and on the nucleon is also presented. Near the 2mπ 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 Cπ+π−A which is consistent with theoretical predictions addressing the partial restoration of chiral symmetry in nuclear matter. Furthermore, the behaviour of Cπ+π−A is well described when the restoration of chiral symmetry is combined with standard P-wave renormalization of pions in nuclear matter. On the other hand, nuclear matter only weakly influences Cπ+π+A, which displays a flat behaviour throughout the energy range regardless of A.

Isospin dependence of the single-particle potential of theΣhyperon in nuclear matter

The isospin dependence of the real part of the single-particle potential of a $\ensuremath{\Sigma}$ hyperon in nuclear matter, ${V}_{\ensuremath{\Sigma}}$ is investigated. The isospin-dependent part ${V}_{1}$ of ${V}_{\ensuremath{\Sigma}}$ is expressed in terms of an effective $\ensuremath{\Sigma}N$ interaction in nuclear matter, which depends on proton and neutron densities. With suitable approximations numerical results for ${V}_{1}$ are obtained for four models of the Nijmegen baryon-baryon interaction. A comparison with recent ${(K}^{\ensuremath{-}},{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$ experiments favors model F as a realistic representation of the $\ensuremath{\Sigma}N$ interaction.