Prof. Teruaki Suyama

The Kramers–Kronig (KK) relations, originating from causality, establish a fundamental link between the real part and imaginary part of any causal response function. In the context of gravitational-wave lensing, these relations provide a powerful and model-independent way to connect the real and the imaginary parts of the amplification factor. In this talk, I will first outline the derivation and reformulation of the KK relations, and then discuss their applications to gravitational lensing of gravitational waves. In particular, I will show how the KK framework can be used to identify lensed gravitational-wave signals without specifying a lens model. This suggests that the KK relations offer a useful diagnostic tool for future gravitational-wave observations.