Microscopic calculations show a strong parity dependence of the nuclear level density at low excitation energy of a nucleus. Previously, this dependence has either been neglected or only implemented in the initial and final channels of Hauser-Feshbach calculations. We present an indirect way to account for a full parity dependence in all steps of a reaction, including the one of the compound nucleus formed in a reaction. To illustrate the impact on astrophysical reaction rates, we present rates for neutron captures in isotopic chains of Ni and Sn. Comparing with the standard assumption of equipartition of both parities, we find noticeable differences in the energy regime of astrophysical interest caused by the parity dependence of the nuclear level density found in the compound nucleus even at sizeable excitation energies.
A simple description for obtaining the parity distribution of nuclear levels in the pf + g9/2 shell as a function of excitation energy was recently derived. We implement this in a global nuclear level density model. In the framework of the statistical model, cross sections and astrophysical reaction rates are calculated in the Fe region and compared to rates obtained with the common assumption of an equal distribution of parities. We find considerable differences, especially for reactions involving particles in the exit channel.
A generalized method to calculate the excitation-energy dependent parity ratio in the nuclear level density is presented, using the assumption of Poisson distributed independent quasi particles combined with BCS occupation numbers. It is found that it is crucial to employ a sufficiently large model space to allow excitations both from low-lying shells and to higher shells beyond a single major shell. Parity ratios are only found to equilibrate above at least 5-10 MeV of excitation energy. Furthermore, an overshooting effect close to major shells is found where the parity opposite to the ground…
Astrophysical reaction rates are sensitive to the parity distribution at low excitation energies. We combine a formula for the energy-dependent parity distribution with a microscopic-macroscopic nuclear level density. This approach describes well the transition from low excitation energies, where a single parity dominates, to high excitations where the two densities are equal.
Proton threshold states in 23Mg are important for the astrophysically relevant proton capture reaction 22Na(p,gamma)23Mg. In the indirect determination of the resonance strength of the lowest states, which were not accessible by direct methods, some of the spin-parity assignments remained experimentally uncertain. We have investigated these states with Shell Model, Coulomb displacement, and Thomas-Ehrman shift calculations. From the comparison of calculated and observed properties we relate the lowest relevant resonance state at E=7643 keV to an excited 3/2+ state in accordance with a recent e…
We present some results and remarks based on a combinatorial approach of the evaluation of the nuclear level density. First, we show that it is possible to extract some reliable information from the output of the program whose rough data present a strong statistical fluctuation from bin to bin. This includes smoothing and evaluation of the desired quantities. After some comments about the spin and parity distributions, we consider the question of the non-equipartition of parities, mainly, at low energies. Finally, we present a simple model to include and test this effect in the computation of …
Parity violating elastic electron scattering on neutron-rich nuclei is described in the framework of relativistic mean-field theory. Self-consistent ground state density distributions of Ne, Na, Ni and Sn isotopes are calculated with the relativistic Hartree- Bogoliubov model, and the resulting neutron radii are compared with available experimental data. For the elastic scattering of 850 MeV electrons on these nuclei, the parity-violating asymmetry parameters are calculated using a relativistic optical model with inclusion of Coulomb distortion effects. The asymmetry parameters for chains of i…
Heavy ion experiments provide important data to test astrophysical models. The high density equation of state can be probed in HI collisions and applied to the hot protoneutron star formed in core collapse supernovae. The Parity Radius Experiment (PREX) aims to accurately measure the neutron radius of $^{208}$Pb with parity violating electron scattering. This determines the pressure of neutron rich matter and the density dependence of the symmetry energy. Competition between nuclear attraction and coulomb repulsion can form exotic shapes called nuclear pasta in neutron star crusts and supernov…
We present the first calculations of proton elastic and inelastic scattering in which the Pauli blocking operator contains the leading non-spherical components as well as the usual spherical (angle-averaged) part. We develop a formalism for including the contributions to the effective nucleon-nucleon interaction from the resulting new G-matrix elements that extend the usual two-nucleon spin structure and may not conserve angular momentum. We explore the consequences of parity conservation, time reversal invariance, and nucleon-nucleon antisymmetrization for the new effective interaction. Chang…
Motivated by recent observational data, the equations of state with the inclusion of strangeness-bearing $Λ$-hyperons and the corresponding properties of neutron stars are studied, based on the covariant density functional (CDF) theory. To this end, we specifically employ the density dependent relativistic Hartree-Fock (DDRHF) theory and the relativistic mean field theory (RMF). The inclusion of $Λ$-hyperons in neutron stars shows substantial effects in softening the equation of state. Because of the extra suppression effect originated from the Fock channel, large reductions on both the star m…
We calculate in this work the rates for the neutrino pair production by nucleon-nucleon bremsstrahlung taking into account the full contribution from a nuclear one-pion-exchange potential. It is shown that if the temperatures are low enough ($T \leq 20 MeV$), the integration over the nuclear part can be done for the general case, ranging from the completely degenerate (D) to the non-degenerate (ND) regime. We find that the inclusion of the full nuclear contribution enhances the neutrino pair production by $nn$ and $pp$ bremsstrahlung by a factor of about two in both the D and ND limits when co…
Extending multi-messenger constraints on neutron star matter through the inclusion of direct Urca cooling
Universität Potsdam（波茨坦大学）；National Research and Innovation Agency (BRIN)（国家研究与创新署）；Utrecht University（乌得勒支大学）；Nikhef（尼赫夫）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））
The parity violating asymmetry $A_{PV}$ in $^{208}$Pb, recently measured by the PREX-2 collaboration, is studied using modern relativistic (covariant) and non-relativistic energy density functionals. We first assess the theoretical uncertainty on $A_{PV}$ which is intrinsic to the adopted approach. To this end, we use quantified functionals that are able to accommodate our previous knowledge on nuclear observables such as binding energies, charge radii, and the dipole polarizability $α_D$ of $^{208}$Pb. We then add the quantified value of $A_{PV}$ together with $α_D$ to our calibration dataset…
We derive the evolution equations for a system of neutrinos interacting among themselves and with a matter background, based upon the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy. This theoretical framework gives an (unclosed) set of first-order coupled integro-differential equations governing the evolution of the reduced density matrices. By employing the hierarchy, we first rederive the mean-field evolution equations for the neutrino one-body density matrix associated with a system of neutrinos and antineutrinos interacting with matter and with an anisotropic neutrino background. Th…
Fundamental differences in the prediction of reaction rates with intermediate and heavy target nuclei compared to the ones with light nuclei are discussed, with special emphasis on stellar modifications of the rates. Ground and excited state contributions to the stellar rates are quantified, deriving a linear weighting of excited state contributions despite of a Boltzmann population of the nuclear states. A Coulomb suppression effect of the excited state contributions is identified, acting against the usual Q-value rule in some reactions. The proper inclusion of experimental data in revised st…
Charged-current neutrino opacity within the relativistic Hartree-Fock framework for astrophysical simulations of core-collapse supernovae and binary neutron star mergers
Wroclaw University of Science and Technology（弗罗茨瓦夫科技大学）；University of Wrocław（弗罗茨瓦夫大学）；Silesian University in Opava（奥帕瓦西里西亚大学）
Probing the three-body force in hadronic systems with specific charge parity
Beihang University（北京航空航天大学）；Lanzhou University（兰州大学）；École Centrale de Pékin/School of General Engineering, Beihang University（北京航空航天大学中法工程师学院/通用工程学院）；Peng Huanwu Collaborative Center for Research and Education, Beihang University（北京航空航天大学彭桓武研究中心）；Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University（北京航空航天大学先进核材料物理北京市重点实验室）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所南方核科学理论中心）
We explore the properties of nuclear pasta appearing in supernova matter, i.e., matter at finite temperature with a fixed proton fraction. The pasta phases with a series of geometric shapes are studied using the compressible liquid-drop (CLD) model, where nuclear matter separates into a dense liquid phase of nucleons and a dilute gas phase of nucleons and $α$ particles. The equilibrium conditions for two coexisting phases are derived by minimization of the total free energy including the surface and Coulomb contributions, which are clearly different from the Gibbs conditions for phase equilibr…
