Extended duality symmetries in theories of gravity

This thesis aims to shed a bit more light on the hidden duality symmetries in theories of gravity. It is well-known that these symmetries are manifest upon compactification to lower dimensions, and in low enough dimensions they are described by infinite-dimensional Kac-Moody algebras. Dualities show that apparently distinct theories are alternative descriptions of one underlying theory. They generate families of new exact solutions (black holes, branes, etc.) systematically from known ones, and strongly-coupled theories may be analysed non-perturbatively via their weakly-coupled dual counterparts. As a result, a non-linear dual gravity theory may be rather crucial for understanding how gravity behaves non-perturbatively at high energies. Across four articles, we investigated duality symmetries in the context of gravity in four dimensions, supergravity in eleven dimensions, non-Lorentzian theories, and exceptional field theory.