标题： 单模方法在宇宙常数问题中的应用 显示英文标题

标题： Unimodular approaches to the cosmological constant problem

摘要： 我们回顾了单模引力的一些方面，并讨论了其作为解决古老宇宙常数问题的可行性。 在单模引力中，宇宙常数被提升为一个全局自由度。 我们强调正确设置初始数据的重要性，以在半经典层面上解决宇宙常数问题。 我们回顾了单模引力量子方面的最新路径积分分析，指出半经典结果同样适用于量子层面。 我们指出，该问题的解决本质上依赖于对时空四体积的全局约束。 这使得该理论与真空能量隔离器密切相关，后者以类似的方式运作。 我们讨论了扩展单模引力的可能途径，这些途径保留了宇宙常数问题的解决方案。 显示英文摘要

摘要： We review selected aspects of unimodular gravity and we discuss its viability as a solution of the old cosmological constant problem. In unimodular gravity the cosmological constant is promoted to a global degree of freedom. We highlight the importance of correctly setting up its initial data in order to achieve a resolution of the cosmological constant problem on a semi-classical level. We review recent path integral analysis of quantum aspects of unimodular gravity to note that the semi-classical findings carry over to the quantum level as well. We point out that a resolution of the problem inherently relies on a global constraint on the space-time four-volume. This makes the theory closely related to the vacuum energy sequester, which operates in a similar way. We discuss possible avenues of extending unimodular gravity that preserve the resolution of the cosmological constant problem.