Possible existence of viable models of bi-gravity with detectable graviton oscillations by gravitational wave detectors

We discuss graviton oscillations based on the ghost-free bi-gravity theory. We point out that this theory possesses a natural cosmological background solution that is very close to the case of general relativity. Furthermore, the interesting parameter range of the graviton mass, which can be explored by observations of gravitational waves, is not at all excluded by the constraint from solar system tests. Therefore, a graviton oscillation with a possible inverse chirp signal would be an interesting scientific target for KAGRA, Advanced LIGO, Advanced Virgo, and GEO.