  We undertake a general study of the boundary (or edge) modes that arise in
gauge and gravitational theories defined on a space with boundary, either
asymptotic or at finite distance, focusing on efficient techniques for
computing the corresponding boundary action. Such actions capture all the
dynamics of the system that are implied by its asymptotic symmetry group, such
as correlation functions of the corresponding conserved currents. Working in
the covariant phase space formalism, we develop a collection of approaches for
isolating the boundary modes and their dynamics, and illustrate with various
examples, notably AdS$_3$ gravity (with and without a gravitational
Chern-Simons terms) subject to assorted boundary conditions.

High Energy Physics - Theory;General Relativity and Quantum Cosmology