Gravitational wave memory in modified gravity theories

Although the permanent distortions of spacetime after the passage of gravitational waves, a phenomenon predicted by Einstein’s General Relativity known as the gravitational wave memory effect, have not yet been observed, its detection is expected in the near future. Such a discovery will serve as an intriguing window into the non-linearity of the theory of gravity and may offer a potent means to scrutinize any potential deviations from Einstein’s predictions. In order to design such future tests of General Relativity, a better understanding of gravitational wave memory in theories beyond is indispensable. The focus of this thesis resides in the exploration of the non-linear gravitational-wave memory effect in general metric theories of gravity through Isaacson’s approach to leading-order field equations. The aim is to explore the impact of additional radiative degrees of freedom on the phenomenon of non-linear memory, within scalar-vector-tensor theories with a non-trivial vector-field background. The beyond General Relativity sector of such theories induces a characteristic departure from the General Relativity prediction and might therefore promote future measurements of non-linear memory as a smoking gun for the presence of additional degrees of freedom beyond General Relativity.