Spatial Correlation of Massive Black Hole Mergers: Probing the Formation   Mechanism and Reionization
  We consider the spatial clustering of massive black hole (MBH) mergers, and discuss possible ways to use gravitational wave observations in the LISA and DECIGO/BBO range for obtaining cosmological and cosmogonical information. Constraints on large scale structure (LSS) and merger histories may be possible by detections of an alignment of the GW polarization direction with principal axes of the LSS. Constraints on the merger physics and the reionization epoch may be obtained by GW measurements of MBH correlation lengths, in the case when the MBH angular momentum loss occurs through gas drag. Such measurements would provide information about the LSS and the reionization epoch, additional to and independent of any obtained from electromagnetic signals, as well as about the astrophysics of MBH mergers. 
Kunihito Ioka, Peter Meszaros