Theory-Agnostic Tests of GR with Multi-Band Gravitational Waves

The aLIGO detection of the black-hole binary GW150914 opened a new era for testing General Relativity in extreme gravity. One generic feature that can be constrained is the emission of dipole gravitational radiation by compact binaries. This is excluded to high accuracy in binary pulsars, but entire classes of gravitational theories predict this effect in binaries predominantly (or only) involving black holes. In this talk, I will describe how future, joint observations of GW150914-like systems by aLIGO and eLISA will dramatically improve bounds on dipole emission from black-hole binaries, probing extreme gravity with unprecedented accuracy.