标题： 协方差和对称代数 显示英文标题

标题： Covariance and symmetry algebras

摘要： 在广义相对论以及规范理论中，边界上可能出现非平凡的对称性。 在存在辐射的情况下，一些对称性不是哈密顿向量场，因此对称性的电荷定义变得复杂。 这可能导致电荷代数中的场依赖的2-上循环问题，而不是标准经典力学中允许的中心扩张。 我们表明，如果实施Wald-Zoupas方案，其协变性要求保证诺特电流的代数没有场依赖的2-上循环，其平稳性要求进一步消除了中心扩张。 因此，电荷代数最多包含一个与时间无关的场依赖的2-上循环，其存在性取决于边界条件。 我们报告了通过这种方法可以推导出的未来null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.