Scalar functions for wave extraction in numerical relativity

Abstract

Wave extraction plays a fundamental role in the binary black hole simulations currently performed in numerical relativity. Having a well-defined procedure for wave extraction, which matches simplicity with efficiency, is critical especially when comparing waveforms from different simulations. Recently, progress has been made in defining a general technique which uses Weyl scalars to extract the gravitational wave signal, through the introduction of the quasi-Kinnersley tetrad. This procedure has been used successfully in current numerical simulations; however, it involves complicated calculations. The work in this paper simplifies the procedure by showing that the choice of the quasi-Kinnersley tetrad is reduced to the choice of the timelike vector used to create it. The spacelike vectors needed to complete the tetrad are then easily identified, and it is possible to write the expression for the Weyl scalars in the right tetrad, as simple functions of the electric and magnetic parts of the Weyl tensor.