Testing Gravitational Theories with Broken Lorentz Symmetry by Gravitational Wave Observations

In this talk, I shall present our recent studies on testing Einstein-aether theory by gravitational wave (GW) observations. In particular, I shall show that the GW observations and stability of black holes already reduce the four coupling constants of the theory to two, and future observations of GWs and quasi-normal modes of black holes shall further reduce the parameter space of the theory.  

Einstein-aether theory is a particular type of the vector-tensor theory, in which the vector field is timelike and unity, so it defines a preferred direction. As a result, it locally breaks the Lorentz symmetry. Yet, it is self-consistent (free of ghosts,  instabilities, and so on), and is consistent with all the observations and experiments. Its Cauchy problem is also well posed. In addition, due  to the presence of the aether, three different species of gravitons, spin-0, spin-1, and spin-2, exist. This will bring dramatical differences in emissions of 

gravitational waves.