@article{KoelschDietrichUjevicetal.2022,
  author    = {K{\"o}lsch, Maximilian and Dietrich, Tim and Ujevic, Maximiliano and Br{\"u}gmann, Bernd},
  title     = {Investigating the mass-ratio dependence of the prompt-collapse threshold with numerical-relativity simulations},
  series = {Physical review : D, Particles, fields, gravitation, and cosmology},
  volume    = {106},
  journal   = {Physical review : D, Particles, fields, gravitation, and cosmology},
  number    = {4},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2470-0010},
  doi       = {10.1103/PhysRevD.106.044026},
  pages     = {27},
  year      = {2022},
  abstract  = {The next observing runs of advanced gravitational-wave detectors will lead to a variety of binary neutron star detections and numerous possibilities for multimessenger observations of binary neutron star systems. In this context a clear understanding of the merger process and the possibility of prompt black hole formation after merger is important, as the amount of ejected material strongly depends on the merger dynamics. These dynamics are primarily affected by the total mass of the binary, however, the mass ratio also influences the postmerger evolution. To determine the effect of the mass ratio, we investigate the parameter space around the prompt-collapse threshold with a new set of fully relativistic simulations. The simulations cover three equations of state and seven mass ratios in the range of 1.0 <= q <= 1.75, with five to seven simulations of binary systems of different total mass in each case. The threshold mass is determined through an empirical relation based on the collapse time, which allows us to investigate effects of the mass ratio on the threshold mass and also on the properties of the remnant system. Furthermore, we model effects of mass ratio and equation of state on tidal parameters of threshold configurations.},
  language  = {en}
}
@article{GiegSchianchiDietrichetal.2022,
  author    = {Gieg, Henrique and Schianchi, Federico and Dietrich, Tim and Ujevic, Maximiliano},
  title     = {Incorporating a Radiative Hydrodynamics Scheme in the Numerical-Relativity Code BAM},
  series = {Universe : open access journal},
  volume    = {8},
  journal   = {Universe : open access journal},
  number    = {7},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2218-1997},
  doi       = {10.3390/universe8070370},
  pages     = {25},
  year      = {2022},
  abstract  = {To study binary neutron star systems and to interpret observational data such as gravitational-wave and kilonova signals, one needs an accurate description of the processes that take place during the final stages of the coalescence, for example, through numerical-relativity simulations. In this work, we present an updated version of the numerical-relativity code BAM in order to incorporate nuclear-theory-based equations of state and a simple description of neutrino interactions through a neutrino leakage scheme. Different test simulations, for stars undergoing a neutrino-induced gravitational collapse and for binary neutron stars systems, validate our new implementation. For the binary neutron stars systems, we show that we can evolve stably and accurately distinct microphysical models employing the different equations of state: SFHo, DD2, and the hyperonic BHB Lambda phi. Overall, our test simulations have good agreement with those reported in the literature.},
  language  = {en}
}
@article{UjevicRashtiGiegetal.2022,
  author    = {Ujevic, Maximiliano and Rashti, Alireza and Gieg, Henrique Leonhard and Tichy, Wolfgang and Dietrich, Tim},
  title     = {High-accuracy high-mass-ratio simulations for binary neutron stars and their comparison to existing waveform models},
  series = {Physical review : D, Particles, fields, gravitation, and cosmology},
  volume    = {106},
  journal   = {Physical review : D, Particles, fields, gravitation, and cosmology},
  number    = {2},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2470-0010},
  doi       = {10.1103/PhysRevD.106.023029},
  pages     = {10},
  year      = {2022},
  abstract  = {The subsequent observing runs of the advanced gravitational-wave detector network will likely provide us with various gravitational-wave observations of binary neutron star systems. For an accurate interpretation of these detections, we need reliable gravitational-wave models. To test and to point out how existing models could be improved, we perform a set of high-resolution numerical relativity simulations for four different physical setups with mass ratios q = 1.25, 1.50, 1.75, 2.00, and total gravitational mass M = 2.7 M???. Each configuration is simulated with five different resolutions to allow a proper error assessment. Overall, we find approximately second-order converging results for the dominant (2,2) mode, but also the subdominant (2,1), (3,3), and (4,4) modes, while generally, the convergence order reduces slightly for an increasing mass ratio. Our simulations allow us to validate waveform models, where we find generally good agreement between state-of-the-art models and our data, and to prove that scaling relations for higher modes currently employed for binary black hole waveform modeling also apply for the tidal contribution. Finally, we also test if the current NRTidal model used to describe tidal effects is a valid description for high-mass-ratio systems. We hope that our simulation results can be used to further improve and test waveform models in preparation for the next observing runs.},
  language  = {en}
}
@article{RashtiFabbriBruegmannetal.2022,
  author    = {Rashti, Alireza and Fabbri, Francesco Maria and Br{\"u}gmann, Bernd and Chaurasia, Swami Vivekanandji and Dietrich, Tim and Ujevic, Maximiliano and Tichy, Wolfgang},
  title     = {New pseudospectral code for the construction of initial data},
  series = {Physical review D},
  volume    = {105},
  journal   = {Physical review D},
  number    = {10},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2470-0010},
  doi       = {10.1103/PhysRevD.105.104027},
  pages     = {18},
  year      = {2022},
  abstract  = {Numerical studies of the dynamics of gravitational systems, e.g., black hole-neutron star systems, require physical and constraint-satisfying initial data. In this article, we present the newly developed pseudospectral code ELLIPTICA, an infrastructure for construction of initial data for various binary and single gravitational systems of all kinds. The elliptic equations under consideration are solved on a single spatial hypersurface of the spacetime manifold. Using coordinate maps, the hypersurface is covered by patches whose boundaries can adapt to the surface of the compact objects. To solve elliptic equations with arbitrary boundary condition, ELLIPTICA deploys a Schur complement domain decomposition method with a direct solver. In this version, we use cubed sphere coordinate maps and the fields are expanded using Chebyshev polynomials of the first kind. Here, we explain the building blocks of ELLIPTICA and the initial data construction algorithm for a black hole-neutron star binary system. We perform convergence tests and evolve the data to validate our results. Within our framework, the neutron star can reach spin values close to breakup with arbitrary direction, while the black hole can have arbitrary spin with dimensionless spin magnitude ∼0.8.},
  language  = {en}
}