Gravitational waves and the polarizations in Ho\v{r}ava gravity after GW170817

Understand

The gravitational waves of Ho\v{r}ava gravity, their polarization states and their possible observational signatures are discussed.

• Using the gauge-invariant variable formalism, we found the three polarization modes in Ho\v{r}ava gravity excited by the three physical degrees of freedom contained in this theory.
• In particular, the scalar degree of freedom excites a mix of the transverse breathing and the longitudinal polarizations.
• The constraints from the previous experimental observations are taken into account, especially including the speed bound from the observations of GW170817 and GRB 170817A.