In gravitational-wave lensing, wave-optical effects become significant when the wavelength is comparable to the lens's characteristic scale. I show causality imposes fundamental constraints on the lensed waveform that go beyond geometric optics and transform it to the Kramers-Kronig relations. I will also discuss application of the KK relations to validating lensed GW candidates in a...
Recent progress in gravitational wave observations has been significant. Pulsar Timing Arrays (PTAs) aims to detect the Gravitational Wave Background (GWB) formed by sources that cannot be individually resolved in the nanohertz band. The sources of the GWB are considered to be orbital motions of Supermassive Black Hole Binaries (SMBHBs). Extracting physical information, such as the mass and...
Recent pulsar timing array (PTA) observations have reported evidence for a gravitational wave background (GWB). If this signal is primarily produced by supermassive black hole binaries (SMBHBs), future PTA observations with the Square Kilometre Array (SKA) are expected to detect multiple continuous gravitational waves (CGWs) from bright individual sources in addition to a stochastic GWB. In...
I will present the joint analyses of Subaru HSC Year 3 (HSC-Y3) cosmic shear 2-point correlation functions (2PCFs), the Planck CMB data, and the ACT DR6 CMB lensing data, that provide insights into history of the structure growth. In Terasawa et al. 2025d, we considered phenomenological modified gravity models in which the suppression of structure growth is triggered at lower redshifts, as...
