Cosmological Bound from the Neutron Star Merger GW170817 in
  scalar-tensor and $F(R)$ gravity theories
  We consider the evolution of cosmological gravitational waves in
scalar-tensor theory and $F(R)$ gravity theory as typical models of the
modified gravity. Although the propagation speed is not changed from the speed
of light, the propagation phase changes when we compare the propagation in
these modified gravity theories with the propagation in the $\Lambda$CDM model.
The phase change might be detected in future observations.
