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Abstract

In the first part of the thesis, we perform a relativistic hydrodynamical simulation of a 1.35-1.35$M_\odot$ binary neutron star (BNS) merger with neutrinos and investigate in detail dynamical mass ejection, ejecta properties and the associated nucleosynthesis calculations. We conduct a systematic study of BNS merger simulations considering different equations of state (EOSs), different total masses, and mass ratios. For a given total mass, comparing the dynamics of postmerger evolution, we observe a systematic decrease in the dominant oscillation frequencies and a relatively quick approximate plateau of maximum densities in the remnants of asymmetric mergers. Additionally, these asymmetric mergers produce higher temperatures, higher average electron fractions, and higher neutrino luminosities in their remnants. Considering ejecta properties, we notice an overall increase in the ejecta mass, the average ejecta temperatures, and a more spherical distribution of the ejecta mass per angular bin. Despite the higher ejecta temperatures, the neutron-richness of the dynamically ejected material from asymmetric mergers is relatively higher than that of symmetric mergers. Specifically, asymmetric mergers are found to produce a larger amount of material ejected from a larger radii of the central remnant that undergo less neutrino irradiation. In the second part of the thesis, we investigate the impact of pions on simulations of neutron star mergers and explore their effects on gravitational wave observables. Compared to models without pions, we observe changes in the properties of cold, non-rotating neutron stars, including reductions in maximum mass, radius, and tidal deformability. From simulations with pions, we find an increase in the dominant post-merger gravitational wave frequency and a reduction of the threshold binary mass for prompt black hole formation. We find empirical relations that correlate the threshold mass or the dominant post-merger gravitational wave frequency to the stellar parameters of nonrotating neutron stars are found to remain valid to good accuracy. Additionally, we also address the mass ejection by neutron star mergers and observe a moderate enhancement of the ejecta mass by the inclusion of pions.