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Register a new userNuclear matter properties at finite temperatures from effective interactions
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We study if commonly used nucleon-nucleon effective interactions, obtained from fitting the properties of cold nuclear matter and of finite nuclei, can properly describe the hot dense nuclear matter produced in intermediate-energy heavy-ion collisions. We use two representative effective interactions, i.e., an improved isospin- and momentum-dependent interaction with its isovector part calibrated by the results from the emph{ab initio} non-perturbative self-consistent Greens function (SCGF) approach with chiral forces, and a Skyme-type interaction fitted to the equation of state of cold nuclear matter from chiral effective many-body perturbation theory and the binding energy of finite nuclei. In the mean-field approximation, we evaluate the equation of state and the single-nucleon potential for nuclear matter at finite temperatures and compare them to those from the SCGF approach. We find that the improved isospin- and momentum-dependent interaction reproduces reasonably well the SCGF results due to its weaker momentum dependence of the mean-field potential than in the Skyrme-type interaction. Our study thus indicates that effective interactions with the correct momentum dependence of the mean-filed potential can properly describe the properties of hot dense nuclear matter and are thus suitable for use in transport models to study heavy-ion collisions at intermediate energies.
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We derive the free energy for fermions and bosons from fragmentation data. Inspired by the symmetry and pairing energy of the Weizsacker mass formula we obtain the free energy of fermions (nucleons) and bosons (alphas and deuterons) using Landaus free energy approach. We confirm previously obtained results for fermions and show that the free energy for alpha particles is negative and very close to the free energy for ideal Bose gases. Deuterons behave more similarly to fermions (positive free energy) rather than bosons. This is due to their low binding energy, which makes them very fragile, i.e., easily formed and destroyed. We show that the {alpha}-particle fraction is dominant at all temperatures and densities explored in this work. This is consistent with their negative free energy, which favors clusterization of nuclear matter into {alpha}-particles at subsaturation densities and finite temperatures. The role of finite open systems and Coulomb repulsion is addressed.
We systematically investigate the vacuum stability and nuclear properties in the effective chiral model with higher order terms in $sigma$. We evaluate the model parameters by considering the saturation properties of nuclear matter as well as the normal vacuum to be globally stable at zero and finite baryon densities. We can find parameter sets giving moderate equations of state, and apply these models to finite nuclei.
Using two-nucleon and three-nucleon interactions derived in the framework of chiral perturbation theory (ChPT) with and without the explicit $Delta$ isobar contributions, we calculate the energy per particle of symmetric nuclear matter and pure neutron matter in the framework of the microscopic Brueckner-Hartree-Fock approach. In particular, we present for the first time nuclear matter calculations using the new fully local in coordinate-space two-nucleon interaction at the next-to-next-to-next-to-leading-order (N3LO) of ChPT with $Delta$ isobar intermediate states (N3LO$Delta$) recently developed by Piarulli et al. [arXiv:1606:06335]. We find that using this N3LO$Delta$ potential, supplemented with a local N2LO three-nucleon interaction with explicit $Delta$ isobar degrees of freedom, it is possible to obtain a satisfactory saturation point of symmetric nuclear matter. For this combination of two- and three-nucleon interactions we also calculate the nuclear symmetry energy and we compare our results with the empirical constraints on this quantity obtained using the excitation energies to isobaric analog states in nuclei and using experimental data on the neutron skin thickness of heavy nuclei, finding a very good agreement with these empirical constraints in all the considered nucleonic density range. In addition, we find that the explicit inclusion of $Delta$ isobars diminishes the strength of the three-nucleon interactions needed the get a good saturation point of symmetric nuclear matter. We also compare the results of our calculations with those obtained by other research groups using chiral nuclear interactions with different many-body methods, finding in many cases a very satisfactory agreement.
We study the properties of $K$ and $bar K$ mesons in nuclear matter at finite temperature from a chiral unitary approach in coupled channels which incorporates the $s$- and p-waves of the kaon-nucleon interaction. The in-medium solution accounts for Pauli blocking effects, mean-field binding on all the baryons involved, and $pi$ and kaon self-energies. We calculate $K$ and $bar K$ (off-shell) spectral functions and single particle properties. The $bar K$ effective mass gets lowered by about -50 MeV in cold nuclear matter at saturation density and by half this reduction at T=100 MeV. The p-wave contribution to the ${bar K}$ optical potential, due to $Lambda$, $Sigma$ and $Sigma^*$ excitations, becomes significant for momenta larger than 200 MeV/c and reduces the attraction felt by the $bar K$ in the nuclear medium.The $bar K$ spectral function spreads over a wide range of energies, reflecting the melting of the $Lambda (1405)$ resonance and the contribution of $YN^{-1}$ components at finite temperature. In the $KN$ sector, we find that the low-density theorem is a good approximation for the $K$ self-energy close to saturation density due to the absence of resonance-hole excitations. The $K$ potential shows a moderate repulsive behavior, whereas the quasi-particle peak is considerably broadened with increasing density and temperature. We discuss the implications for the decay of the $phi$ meson at SIS/GSI energies as well as in the future FAIR/GSI project.
We give a short review of the quark-meson coupling (QMC) model, the quark-based model of finite nuclei and hadron interactions in a nuclear medium, highlighting on the relationship with the Skyrme effective nuclear forces. The model is based on a mean field description of nonoverlapping nucleon MIT bags bound by the self-consistent exchange of Lorentz-scalar-isoscalar, Lorentz-vector-isoscalar, and Lorentz-vector-isovector meson fields directly coupled to the light quarks up and down. In conventional nuclear physics the Skyrme effective forces are very popular, but, there is no satisfactory interpretation of the parameters appearing in the Skyrme forces. Comparing a many-body Hamiltonian generated by the QMC model in the zero-range limit with that of the Skyrme force, it is possible to obtain a remarkable agreement between the Skyrme force and the QMC effective interaction. Furthermore, it is shown that 3-body and higher order N-body forces are naturally included in the QMC-generated effective interaction.
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