Title: Interacting Gravitational Waves
Gravitational waves (GWs) allow us to probe the content of the Universe and the behaviour of gravity on cosmological scales, through information contained in their propagation. For instance, the presence of dynamical fields interacting non-minimally with gravity may induce a non-trivial propagation of GWs, changing their propagation speed, dispersion relation, or detected amplitude, among others. In this talk, I will discuss particular cosmological scenarios where GWs interact with another tensor field, such as in the theory of massive bigravity. I will illustrate explicitly how the GW signal from a coalescence of black holes gets distorted during propagation, generating specific features such as echoes of the GW signal emitted. These strong features suggest that stringent constraints on interacting GWs can be placed with current and future GW detectors.