About this Research Topic
The nature of asymmetric nuclear matter is essentially governed by the density dependence of the symmetry energy, a behavior that is still quite unknown, especially at supra-saturation densities. Quantities like the neutron skin thickness or the neutron star radius are very dependent on the symmetry energy. Recently, PREXII results were published (D. Adhikari, 2021), and a preliminary analysis (B.T. Reed et al, 2021) puts the slope of the symmetry energy L in the range 106\pm 37 MeV, though there are now other works that give L lower values, L=85.5\pm 22.2 MeV (Yue et al.) or L=58\pm 19 MeV (Essick et al.). Another recent experimental finding is the measurement of the spectra of charged pions (J. Estee et al, 2021) that estimates L to be in the range 42 < L < 117 MeV, compatible with PREXII. On the astrophysics side, it is expected, given the very compact nature of neutron stars, that exotic matter, like hyperons or even deconfined quark matter, appear in the core of these objects. The onset of hyperons has proven to be sensitive to many factors, like the slope of the symmetry energy, the nucleon-hyperon interaction, and the many-body interactions between nucleons and hyperons. The (non)existence of hyperons inside neutron stars has been questioned though because such an EoS might not be able to predict very massive stars like PSR J1614-2230, PSR J0348+0432, or MSP J0740+6620. This has been called the "hyperon puzzle". However, one may argue that this problem could be controlled by e.g. using EoS that are hard enough at high densities.
This Research Topic is devoted to the current status of research on the density dependence of the symmetry energy at high densities and the composition of neutron stars, two issues that still remain open questions nowadays. The present Research Topic will gather different views around these topics, having in mind the appearance of new ideas and/or collaborations that might impel the development of the field. Its content will cover several topics closely related with these two issues.
This Research Topic welcomes manuscripts around themes including, but not limited to, the following:
1. the equation of state of nuclear matter and its composition
2. neutron star composition, properties
3. the density dependence of the symmetry energy
4. theoretical description of dense matter at zero and finite temperature
5. experimental measurement of hyperclusters
6. experimental measurements related to the density dependence of the symmetry energy
7. symmetry energy and heavy-ion collisions
8. constraining symmetry energy from Astrophysics
9. cooling mechanism of neutron stars
10. Microscopic hyperonic matter calculations
Keywords: nuclear astrophysics, neutron stars, nuclear matter, equation of state, symmetry energy, hyperonic interaction, hyperonic matter
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