Theory-Agnostic Constraints on Black-Hole Dipole Radiation with
  Multi-Band Gravitational-Wave Astrophysics
  The aLIGO detection of the black-hole binary GW150914 opened a new era for
probing extreme gravity. Many gravity theories predict the emission of dipole
gravitational radiation by binaries. This is excluded to high accuracy in
binary pulsars, but entire classes of theories predict this effect
predominantly (or only) in binaries involving black holes. Joint observations
of GW150914-like systems by aLIGO and eLISA will improve bounds on dipole
emission from black-hole binaries by six orders of magnitude relative to
current constraints, provided that eLISA is not dramatically descoped.
