Coexistence of Anderson-Bogoliubov phonon and quadrupole cluster vibration in the inner crust of neutron stars
| Autor: | Tsunenori Inakura, Masayuki Matsuo |
|---|---|
| Rok vydání: | 2019 |
| Předmět: |
Physics
Condensed matter physics 010308 nuclear & particles physics Phonon Astrophysics::High Energy Astrophysical Phenomena Nuclear Theory 01 natural sciences Resonance (particle physics) Superfluidity Neutron star 0103 physical sciences Quadrupole Quasiparticle Neutron 010306 general physics Random phase approximation |
| Zdroj: | Physical Review C. 99 |
| ISSN: | 2469-9993 2469-9985 |
| Popis: | Background: Low-lying collective excitations of the inner crust matter in neutron stars are expected to affect observables such as the quasiperiodic oscillation in giant flares or cooling of the inner crust in transient phenomena. The coupling between the Anderson-Bogoliubov (AB) superfluid phonon in superfluid neutron gas and collective excitations of nuclear clusters is crucially important.Purpose: Our aim is to describe the characteristics of the low-lying excitation modes of the superfluid inner crust matter, focusing on quadrupole excitations around a spherical nuclear cluster. We studied the effect of the inhomogeneous structure of the inner crust matter on the AB phonon of neutron superfluid and on the possible quadrupole shape vibration of clusters.Methods: The coordinate-space Hartree-Fock-Bogoliubov method and the quasiparticle random phase approximation formulated in a spherical Wigner-Seitz cell were used to describe the neutron superfluidity and low-lying collective excitations. We performed systematic numerical calculations for the quadrupole excitations by varying the neutron chemical potential and the number of protons in the cell.Results: The calculated results indicate the appearance of both AB phonon and quadrupole shape vibration of the cluster with small mixing between the two collective modes. The quadruple AB phonon is similar to that in the uniform superfluid, apart from the small admixture of the shape vibration of cluster. The excitation energy and the collectivity of the cluster vibration mode show a strong and oscillatory dependence on the neutron chemical potential (the neutron gas density), resulting in softening and instability under certain conditions. This is due to the resonance shell effect, where unbound, but resonant single-particle states of neutrons are crucially important.Conclusions: The AB phonon of the superfluid neutron gas and the quadrupole shape vibration of the nuclear cluster coexist in the inner crust. The coupling between the AB phonon and the quadrupole shape vibration is weak. The collectivity of the quadrupole shape vibration is controlled by the resonance shell effect, which suggests that the appearance of deformed nuclear clusters is possible in any layer of the inner crust. |
| Databáze: | OpenAIRE |
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