Testing Einstein-Aether Theory by Gravitational Wave Observations

Gravitationally bound hierarchies containing three or more components are very common, and many of them should be detected by the advanced LIGO/Virgo, KAGRA and LISA. In this talk, I present our recent studies on the emissions of periodic gravitational waves (GWs) in Einstein-aether theory, which violates the Lorentz symmetry, yet satisfies all the theoretical and observational constraints carried out so far.

In particular, I shall first show that, in the weak-field approximations and with the current constraints, the strong-field effects for a binary system of neutron stars are about six orders lower than that of GR. Ignoring these effects I present the general formulas of the theory to the lowest post-Newtonian order, by taking the coupling of the aether field with matter into account. Then, I shall show that the scalar breather and longitudinal modes are all suppressed by a factor of $10^{-5}$ with respect to the transverse-traceless modes, while the vectorial modes are suppressed by a factor of $10^{-15}$. Applying the general formulas to a triple system, I shall show that the corresponding GW forms, response functions, and their Fourier transforms all depend sensitively on the configurations of the triple systems and binding energies of the 3-bodies.