Abstract:
Pulsar timing array searches for the stochastic gravitational wave background at nano-Hertz frequencies are now beginning to reach astrophysically interesting sensitivities, placing more and more stringent constraints on the strength of the background. The strength and spectral shape of the background contain information about the underlying population of merging massive black hole binaries in the Universe, for example the merger rate density and the mass and redshift distributions. Here, we are using a generic model with minimal assumptions to investigate what we can learn about the population of merging massive black holes from current upper limits and possible future detections of the gravitational wave background.