Graviton Mass Bounds
  Recently, aLIGO has announced the first direct detections of gravitational
waves, a direct manifestation of the propagating degrees of freedom of gravity.
The detected signals GW150914 and GW151226 have been used to examine the basic
properties of these gravitational degrees of freedom, particularly setting an
upper bound on their mass. It is timely to review what the mass of these
gravitational degrees of freedom means from the theoretical point of view,
particularly taking into account the recent developments in constructing
consistent massive gravity theories. Apart from the GW150914 mass bound, a few
other observational bounds have been established from the effects of the Yukawa
potential, modified dispersion relation and fifth force that are all induced
when the fundamental gravitational degrees of freedom are massive. We review
these different mass bounds and examine how they stand in the wake of recent
theoretical developments and how they compare to the bound from GW150914.
