Asymptotic flatness at null infinity in arbitrary dimensions
  We define the asymptotic flatness and discuss asymptotic symmetry at null infinity in arbitrary dimensions using the Bondi coordinates. To define the asymptotic flatness, we solve the Einstein equations and look at the asymptotic behavior of gravitational fields. Then we show the asymptotic symmetry and the Bondi mass loss law with the well-defined definition. 
Kentaro Tanabe, Shunichiro Kinoshita and Tetsuya Shiromizu
gr-qc hep-th