标题： 广义协变性和边界对称代数 显示英文标题

标题： General covariance and boundary symmetry algebras

摘要： 在广义相对论以及规范场理论中，非平凡的对称性可能出现在边界上。 在存在辐射的情况下，部分对称性不再是哈密顿矢量场，因此对这些对称性的荷的定义变得微妙起来。 这可能导致荷代数中出现场相关的 2-上循环问题，与标准经典力学中允许的中心扩展形成对比。 我们证明，如果实施 Wald-Zoupas 处方，则其协变性要求保证诺特流的代数不含场相关的 2-上循环，而其平稳性要求进一步消除了中心扩展。 因此，荷代数最多只能具有时间无关的场相关 2-上循环，其存在依赖于边界条件。 我们报告了通过这种方法可以得到的关于未来零无穷远处渐近对称性的新结果。 显示英文摘要

摘要： In general relativity as well as gauge theories, non-trivial symmetries can appear at boundaries. In the presence of radiation some of the symmetries are not Hamiltonian vector fields, hence the definition of charges for the symmetries becomes delicate. It can lead to the problem of field-dependent 2-cocycles in the charge algebra, as opposed to the central extensions allowed in standard classical mechanics. We show that if the Wald-Zoupas prescription is implemented, its covariance requirement guarantees that the algebra of Noether currents is free of field-dependent 2-cocycles, and its stationarity requirement further removes central extensions. Therefore the charge algebra admits at most a time-independent field-dependent 2-cocycle, whose existence depends on the boundary conditions. We report on new results for asymptotic symmetries at future null infinity that can be derived with this approach.