Sommaire:

In the fully nonlinear regime, gravitational waves can reveal a drastic new phenomenology absent in the linearized theory. This is best illustrated by investigating exact non-perturbative radiative solutions of General Relativity. When new fields are introduced, such as in modified scalar-tensor theories, the scalar-tensor mixing can drastically modify the phenomenology of gravitational waves. So far, most of the efforts have focused on investigating the effects of these scalar-tensor mixing at the perturbative level.
In this talk, I will present a new exact radiative solution in Horndeski gravity describing the nonlinear gravitational waves emitted by a scalar pulse. I will use this opportunity to describe the non-perturbative methods allowing to analyze the gravitational wave content of a given spacetime geometry (Petrov classification, Penrose limit). Then, I will discuss how this exact new solution can be constructed using the disformal solution-generating map and comment on its new phenomenology. In particular, this analysis will show that in such higher order scalar-tensor theory, shear (tensorial modes) can be generated by a purely (time-dependent) scalar monopole, a feature which only emerges at the fully nonlinear level.
This work aims at providing a tractable toy model to explore the nonlinear radiative regime of modified gravity theories. The talk will be based on the following article: https://arxiv.org/abs/2401.05099

Pour plus d'informations, merci de contacter Lavalle J.