GRASS Seminar: BMS algebra and supertranslation-invariant Lorentz charges

The BMS algebra implies the puzzling feature that the standard Lorentz charges are not invariant under BMS supertranslations. This makes the definitions of the angular momentum and angular momentum flux somewhat obscure. We provide a definition of the Lorentz charges that is supertranslation invariant.  In order to preserve a full canonical structure, it is necessary to introduce logarithmic BMS supertranslations. Also to be pointed out is that the required redefinitions turn out to be non linear.