标题： 在广义Proca理论及之外反弹或不反弹 显示英文标题

标题： To bounce or not to bounce in generalized Proca theory and beyond

摘要： 众所周知，构建一个在整个宇宙演化过程中避免所有可能不稳定的稳定非奇异反弹宇宙学模型是非常困难的。 在这项工作中，我们探讨了是否可以通过广义相对论的一种特定修改，即矢量张量广义Proca理论来构造一个没有遇到线性扰动理论中任何病态现象的非奇异反弹。 我们发现，这样的模型不可避免地会导致张量或标量部分出现强耦合，或者反弹阶段物质部分出现不稳定性。 由于我们的分析是以规范无关的方式进行的，这一结果可以表述为关于具有广义Proca的非奇异反弹的一个不可能定理。 然而，与Horndeski理论中找到的不可能定理不同，通过考虑超出广义Proca理论并不能规避这一结论。 我们结果的核心在于矢量场的时间分量的非动力学性质，这使得它不适合作为反弹解的媒介。 显示英文摘要

摘要： It is notoriously difficult to construct a stable non-singular bouncing cosmology that avoids all possible instabilities throughout the entire evolution of the universe. In this work, we explore whether a non-singular bounce driven by a specific class of modifications of General Relativity, the vector-tensor generalized Proca theories, can be constructed without encountering any pathologies in linear perturbation theory. We find that such models unavoidably lead either to strong coupling in the tensor or the scalar sector, or instabilities in the matter sector during the bouncing phase. As our analysis is performed in a gauge-independent way, this result can be cast in the form of a no-go theorem for non-singular bounces with generalized Proca. In contrast to the no-go theorem found for Horndeski theories, however, it cannot be evaded by considering beyond generalized Proca theory. At the core of our result lies the non-dynamical nature of the temporal component of the vector field, which renders it an ill-suited mediator for a bouncing solution.