Logarithmic supertranslations and supertranslation-invariant Lorentz charges

Understand

We extend the BMS(4) group by adding logarithmic supertranslations.

• This is done by relaxing the boundary conditions on the metric and its conjugate momentum at spatial infinity in order to allow logarithmic terms of carefully designed form in the asymptotic expansion, while still preserving finiteness of the action.
• Standard theorems of the Hamiltonian formalism are used to derive the (finite) generators of the logarithmic supertranslations.
• As the ordinary supertranslations, these depend on a function of the angles.