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The Role of the Equation of State in Core-Collapse Supernovae, Neutron Stars and their mergers

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2019, Doctor of Philosophy (PhD), Ohio University, Physics and Astronomy (Arts and Sciences).
The equation of state (EOS) of dense matter is a crucial input in simulations of core-collapse supernovae, evolution of neutron stars from their birth to old age and binary neutron star mergers. The EOS is required over wide ranges of density and temperature, as well as under conditions in which neutrinos are trapped, and in the presence of intense magnetic field, and rapid differential and subsequent rigid rotation. In the three research projects included in this dissertation, I have made several advances in the EOS modeling. In the first project, I employed the formalism of next-to-leading order Fermi Liquid Theory to calculate the thermal properties of symmetric nuclear and pure neutron matter. The advantage here is that only the single-particle energy spectrum at zero temperature is required to calculate the thermal properties under conditions of high degeneracy. The method was applied to a relativistic many-body theory beyond the mean field level which includes exchange (two-loop) effects. For all thermal variables, the semi-analytical next-to-leading order corrections reproduced results of the exact numerical calculations for entropies per baryon up to $2k_B$, where $k_B$ is the Boltzmann constant. Excellent agreement was found down to subnuclear densities for temperatures up to $20$ MeV. In addition to gaining physical insights, a rapid evaluation of the EOS in the homogeneous phase of hot and dense matter was achieved through the use of the zero-temperature Landau effective mass function and its derivatives. The second project I was a part of was concerned with neutron star mergers, the first of which in the observed astronomical event termed GW170817 \cite{Abbott1} has been recently reported through the detection of gravitational waves. Here, a critical assessment of the current status of dense matter theory was made. In addition, I and my collaborators have pointed out the successes and limitations of the approaches currently in use along with suggestions made for improvements in several areas. The new development in this project was the generalization of the excluded volume approach to include multiple clusters such as deuteron $(d)$, triton ($^3$H) and helium-3 ($^3$He) in addition to $\alpha$-particles previously considered. This inclusion is necessary to properly account for electron capture and neutrino scattering in subnuclear-density matter as observable signals are formed in this region. The role of trapped neutrinos, magnetic fields and rotation (rigid and differential) were also highlighted in this work. The third project addressed the issue of the hadron-to-quark transition within neutron stars. First principle calculations of this transition are not yet available, hence several scenarios such as first- and second-order phase transitions and crossover transitions have been explored in the literature. In this work, a detailed comparative study was performed by examining the results pertaining to neutron structure; that is, the masses and radii of neutron stars which depend on the treatment of the transition employed. Hadronic EOSs consistent with the nuclear systematics at nuclear densities were employed and several models of the quark matter EOS were explored. In all cases, consistency with the observational constraints provided by well-measured neutron star masses, estimates of radii from x-ray observations and bounds on tidal deformations set by the recent gravitational wave detection in GW170817 was sought. This work has enabled us to identify the class of EOSs in both the hadronic and quark sectors as well as specify the conditions in which one or the other treatment of the transition to quark matter may be appropriate. The published papers stemming from the first two projects and the manuscript of the third project submitted for publication are reproduced verbatim in this thesis. The abstracts and contents therein provide additional technical details.
Prakash Madappa (Advisor)
Hee-Jong Seo (Committee Member)
Alexander Neiman (Committee Member)
Jessica White (Committee Member)
186 p.

Recommended Citations

Citations

  • Lalit, S. S. (2019). The Role of the Equation of State in Core-Collapse Supernovae, Neutron Stars and their mergers [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1564056399895895

    APA Style (7th edition)

  • Lalit, Sudhanva. The Role of the Equation of State in Core-Collapse Supernovae, Neutron Stars and their mergers. 2019. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1564056399895895.

    MLA Style (8th edition)

  • Lalit, Sudhanva. "The Role of the Equation of State in Core-Collapse Supernovae, Neutron Stars and their mergers." Doctoral dissertation, Ohio University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1564056399895895

    Chicago Manual of Style (17th edition)