Improving the convergence order of binary neutron star merger simulations in the Baumgarte- Shapiro-Shibata-Nakamura formulation

High-accuracy numerical relativity simulations of binary neutron star mergers are a necessary ingredient for constructing gravitational-waveform templates to analyze and interpret observations compact object mergers. Numerical convergence in the postmerger phase such is challenging achieve with many modern codes. In this paper, we study two ways improving properties merger within Baumgarte-Shapiro-Shibata-Nakamura formulation Einstein's equations. We show that discontinuities particular constraint damping scheme can destroy simulation. A continuous prescription, contrast, ensures until late times. additionally impact equation state parametrization on premerger simulations. particular, compare results piecewise polytropic parametrization, which commonly used but suffers unphysical sound speed, using ``generalized'' was designed ensure both continuity differentiability state. report differences gravitational waves any spurious heating, depending used.