Gravitational wave extraction in higher dimensional numerical relativity using the Weyl tensor

TL;DR

This paper develops a numerical method to extract gravitational waves in higher-dimensional spacetimes using the Weyl tensor, enabling analysis of black hole collisions beyond four dimensions, with results consistent with existing perturbative techniques.

Contribution

It introduces a new numerical implementation based on Weyl tensor projections for gravitational wave extraction in higher dimensions, extending previous theoretical formalisms.

Findings

Successfully applied to D=6 black hole collisions

Radiated energy fraction matches literature results

Method captures all multipole contributions automatically

Abstract

Gravitational waves are one of the most important diagnostic tools in the analysis of strong-gravity dynamics and have been turned into an observational channel with LIGO's detection of GW150914. Aside from their importance in astrophysics, black holes and compact matter distributions have also assumed a central role in many other branches of physics. These applications often involve spacetimes with $D>4$ dimensions where the calculation of gravitational waves is more involved than in the four dimensional case, but has now become possible thanks to substantial progress in the theoretical study of general relativity in $D>4$. Here, we develop a numerical implementation of the formalism by Godazgar and Reall (Ref.[1]) -- based on projections of the Weyl tensor analogous to the Newman-Penrose scalars -- that allows for the calculation of gravitational waves in higher dimensional spacetimes with rotational symmetry. We apply and test this method in black-hole head-on collisions from rest in $D=6$ spacetime dimensions and find that a fraction $(8.19\pm 0.05)\times 10^{-4}$ of the Arnowitt-Deser-Misner mass is radiated away from the system, in excellent agreement with literature results based on the Kodama-Ishibashi perturbation technique. The method presented here complements the perturbative approach by automatically including contributions from all multipoles rather than computing the energy content of individual multipoles.