Both for studies of cosmic censorship and for practical purposes in gravitational wave astronomy, it is desirable to include future null-infinity in the computational domain. Extending formulations of general relativity known to behave well in the strong-field regime out to infinity with compactification is, however, a subtle game. In my presentation I will explain how the competition between...

I will review the use of numerical relativity to probe cosmological spacetimes, highlighting the particular challenges faced in such simulations compared to the asymptotically flat case associated with black holes. I will focus on its potential to inform the "inflation versus bounce" debate, as an illustration of these challenges.

In this talk, I will present the recent progress of numerical modeling of compact binary mergers, which involves at least one neutron star in numerical relativity. Our group develops self-consistent modelings by performing a long-term numerical relativity neutrino-radiation magnetohydrodynamic simulation. I will present the details of the simulation results and perspective.

Numerical-relativity simulations are prerequisites for a reliable interpretation of multi-messenger events such as binary neutron star or black hole neutron star mergers. When using simulation results to interpret observational data, it is of uttermost importance to also ensure a proper discussion of the uncertainties of the simulations. Keeping this in mind, we show some of our most recent...

We discuss the postmerger stage of binary neutron star coalescences. We present an analytic model of postmerger gravitational-wave emission, which achieves an overall good description of the gravitational-wave signal. The physical parameters of the model are useful to understand the dynamics of the system, and we identify new mechanisms shaping the gravitational-wave spectrum. Moreover, we...

Conservative finite difference methods have proven extremely robust and reliable for magnetohydrodynamics simulations of binary neutron star mergers. However, finite difference methods are generally less accurate and efficient than spectral methods when the solution is smooth, e.g. away from the stellar surfaces. The attractiveness of spectral methods has been demonstrated by thousands of long...

Numerical relativity has been a frontier problem in computational science for over fifty years. The complexity of this research field spans multiple areas, from the properties of partial differential equations to high performance computing. As gravitational wave detectors continually improve, and new detectors come online, a new challenge will be to compute waveforms with higher fidelity and...

Supplementing General Relativity (GR) with an additional scalar degree of freedom yields to a simple and popular class of gravitational theories known as scalar-tensor theories. While scalar-tensor theories can produce self-accelerated cosmic expansion without a cosmological constant, they typically produce also local deviations from GR on small scales. However, some theories possess...

In this talk I will discuss recent progress on modelling black hole binaries in higher derivative theories of gravity. I shall consider first cubic Horndeski theories for which the higher derivatives are in the scalar sector only. In these theories in the weakly coupled regime, even though the differences with standard general relativity can be locally small, they accumulate over the lifetime...

We present numerical simulations of boson-star binary systems and extract the gravitational waves emitted by these systems. We discuss numerical methods and with particular focus on improved initial data and the spurious effects that may result from inappropriate choices for the construction of initial data.