Center of Gravity Seminar: Serena Giardino

Title:Testing modified gravity with gravitational wave lensing

Abstract:Gravitational waves are inevitably lensed as they propagate through the universe, leading to deflection, magnification, and novel interactions between GW polarizations, which can produce distinctive signatures of modified gravity theories. In particular, scalar-tensor models with screening mechanisms, such as symmetron gravity, introduce effective mass terms for GWs and result in lens-induced dispersion, a frequency-dependent phase shift of the waveform. This dispersive effect can be significantly enhanced in screened environments and may, in extreme cases, inhibit GW propagation through certain astrophysical bodies, effectively turning them into reflectors. I will present a formalism that extends beyond the geometric optics approximation, enabling precise characterization of these phenomena and opening up novel avenues to use gravitational wave lensing as a testing ground for theories of dynamical dark energy.