Gravity Seminars

Just like light, gravitational waves (GWs) are gravitationally lensed by massive objects in the Universe. Moreover, their low frequency, phase coherence, and lack of absorption make GWs complementary to lensed electromagnetic sources. In addition to gravitational magnification and the formation of multiple images, lensed GWs exhibit genuine wave-propagation effects such as diffraction, i.e., the bending of the signal’s wavefront. Lensing diffraction imprints a frequency-dependent modulation on the signal, encoding information about the lens mass and its distribution. I will describe the rich phenomenology of lensing diffraction as a means to discover high-redshift, magnified binary mergers and to probe small-scale structures, including dark matter. In theories beyond GR, novel propagation effects such as birefringence and dispersio (polarization- and frequency-dependent phase shifts) provide new tests of cosmological gravity and dynamical dark energy. In addition to recent theoretical developments, I will present the latest analysis of GW231123, the first candidate for a diffracted and magnified compact binary coalescence.