Gravitational Waves in Brane World -A Midi-superspace Approach-
  It is important to reveal the brane-bulk correspondence for understanding the brane world cosmology. When gravitational waves exist in the bulk, however, it is difficult to make the analysis of the interrelationship between the brane and the bulk. Hence, the minimal model which allows gravitational waves in the bulk would be useful. As for such models, we adopt the Bianchi type midi-superspace models. In particular, the effects of gravitational waves in the bulk on the brane cosmology is examined using the midi-superspace approach. 
Jiro Soda