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Nuclei, Nucleons and Quarks in Astrophysical Phenomena

Al Mamun, Md Abdullah
http://orcid.org/0000-0002-2655-1244
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461

Abstract Details

2019, Doctor of Philosophy (PhD), Ohio University, Physics and Astronomy (Arts and Sciences).
The work presented in this dissertation is concerned with properties of nuclei, their internal constituents, nucleons and quarks, of which nucleons are made, in the astrophysical settings of nucleosynthesis, core-collapse supernovae, neutron stars and their mergers. Through energetic considerations, nuclei far-off the stability line are expected to be encountered in all of the arenas mentioned above. Properties of some of these nuclei are expected to be measured in upcoming rare-isotope laboratories across the world. Focussing on the pairing properties of extremely proton- or neutron-rich nuclei, a means to set bounds on their pairing energies was devised in the published work reported here. These bounds were achieved through the introduction of a new model, the Random Spacing Model, in which single-particle energy levels randomly distributed around the Fermi surface of a nucleus were employed. This arrangement ensured that it would encompass predictions of all possible energy density functionals currently being employed. Another new feature of this model is the inclusion of pairing gap fluctuations that go beyond the commonly used mean field approach of determining pairing energies of nuclei. These features, when combined together, enabled us to reproduce the S-shaped behavior of the heat capacity measured in laboratory nuclei. In future work, nuclear level densities, which depend sensitively on pairing energies at low excitation energies, will be calculated using the Random Spacing Model with the inclusion of pairing fluctuations. For baryon densities below about two thirds the central density of heavy nuclei, a mixture of light nuclear clusters such as ${\rm \alpha}$, ${\rm d}$, ${\rm t}$, etc., are favored to be present along with nucleons (neutrons and protons), charge balancing electrons, and heavy nuclei. The concentration of each species is determined by minimizing the free energy density of the system with respect to baryon density, electron fraction and temperature. The new element of our published work in this density region was to generalize the familiar excluded volume approach that considered $\alpha$-particles as representative of all of the light nuclear clusters. Comparisons with the alternative virial expansion approach were made, and the strengths and drawbacks of each approach were critically assessed. In on-going work, a new mean field approach that uses the Hartree-Fock approximation is being developed to overcome the shortcomings of the above two approaches. Its importance lies in the fact that the observed emergent neutrino and photon spectra in astrophysical phenomena are shaped by the low density regions of stellar exteriors. At the supra-nuclear densities encountered in neutron stars, the possibility that quark degrees of freedom may be liberated from their confining hadrons (baryons and mesons) ever since the theory of strong interactions, Quantum Chromo Dynamics (QCD), was put forth in the early 1970's. However, the precise nature of the hadron-to-quark transition is not known at finite baryon densities due to technical difficulties encountered in first-principle calculations. Thus, various scenarios including a first-order phase transition, a second-order phase transition and a smooth crossover transition have been put forth. In work submitted for publication, we have examined many of these scenarios critically by imposing constraints from observations of neutron star masses and tidal deformations obtained in binary neutron star mergers. Our findings are that the equations of state employed in both the hadronic and quark sectors are important in reaching reasonable conclusions. It has become clear that only the masses and radii of neutron stars are insufficient to ascertain the detailed composition of neutron star structure, but consistency with the cooling histories of neutron stars, their spin periods and their derivatives, and other measured properties is also required. Suggestions for further work in this regard are offered in this dissertation.
Madappa Prakash (Advisor)
Zach Meisel (Committee Member)
Steven Grimes (Committee Member)
195 p.
Astrophysics; Nuclear Physics; Physics; Theoretical Physics
Nuclei; nucleons; quarks; astrophysics; nuclear physics; neutron stars; gravitational waves; phase transition; Love number; dense matter; cold dense matter; QCD phase transition; level density; pairing properties; superconductivity; superfluidity

Recommended Citations

Citations

  • Al Mamun, M. A. (2019). Nuclei, Nucleons and Quarks in Astrophysical Phenomena [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461

    APA Style (7th edition)

  • Al Mamun, Md Abdullah. Nuclei, Nucleons and Quarks in Astrophysical Phenomena. 2019. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461.

    MLA Style (8th edition)

  • Al Mamun, Md Abdullah. "Nuclei, Nucleons and Quarks in Astrophysical Phenomena." Doctoral dissertation, Ohio University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461

    Chicago Manual of Style (17th edition)

ohiou1563991151449461
411
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This open access ETD is published by Ohio University and OhioLINK.