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We study nontrivial diffeomorphisms and associated soft charges and symmetries on the bifurcate horizon of a four dimensional Kerr black hole. We first analyze the most general falloff behavior for metric perturbations near the bifurcation surface in the Kruskal type coordinates. The associated algebra of charges is obtained to be two dimensional diffeomorphisms, `` superrotations'' plus two ``scalar supertranslations''. Next, we consider a similar problem for a generic point on the future horizon, away from the bifurcation surface.
In this case the scalar supertranslations are enhanced to become time dependent charges which are also non-integrable. We separate the integrable and non-integrable parts of charge variations using the notion of a modified bracket, and/or the generalized Wald-Zoupas analysis. We find that the non-integrable part of charge variation is time derivative of the integrable charges. The algebra of the integrable part of the charges, which we dub as ``super T-Witts'', at any given point on the bifurcation surface form BMS$_3$ with scalar supertranslations. We comment on the (absence of the) central charge for our charge algebras.
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