We propose a consistent set of boundary conditions for gravity in asymptotically flat spacetime at spacelike infinity, which yields an enhancement of the Bondi-Metzner-Sachs group with smooth superrotations and new subleading symmetries. These boundary conditions are obtained by allowing fluctuations of the boundary structure which are responsible for divergences in the symplectic form, and a renormalization procedure is required to obtain finite canonical generators. The latter are then made integrable by incorporating boundary terms into the symplectic structure, which naturally derive from a linearized spin-two boundary field on a curved background with positive cosmological constant. Finally, we show that the canonical generators form a nonlinear algebra under the Poisson bracket and verify the consistency of this structure with the Jacobi identity.

中文翻译：

---

类空间无限远的超旋转


我们提出了类空无穷远渐近平坦时空中重力的一组一致的边界条件，这产生了具有平滑超旋转和新的次引导对称性的 Bondi-Metzner-Sachs 群的增强。这些边界条件是通过允许边界结构的波动来获得的，边界结构是辛形式发散的原因，并且需要重正化过程来获得有限的正则生成器。然后，通过将边界项合并到辛结构中，使后者可积，辛结构自然地源自具有正宇宙学常数的弯曲背景上的线性化自旋二边界场。最后，我们证明了规范生成元在泊松括号下形成了一个非线性代数，并验证了该结构与雅可比恒等式的一致性。