论文标题
外部曲率有限的理论和非电源各向异性宇宙
Theories with limited extrinsic curvature and a nonsingular anisotropic universe
论文作者
论文摘要
我们提出了一类可以限制从外部曲率构建的标量的理论。该框架应用于宇宙学，使我们不仅可以控制哈勃参数，而且可以控制无ostrogradsky Ghost问题的各向异性，这与限制时空曲率标量的情况形成了鲜明的对比。我们的理论可以被视为模拟和库斯卡顿理论的概括（从而阐明它们的关系），该理论众所周知，它们具有仅在同质和各向同性背景上限制哈勃参数的结构。作为我们框架的应用，我们构建了一个模型，其中各向异性和哈勃参数都在对角Bianchi I型I设置中的宇宙演变中的任何阶段保持有限。宇宙从恒定的肛门拷贝阶段开始，并在低能量下恢复了爱因斯坦重力。我们还表明，宇宙学解决方案对广泛的扰动波数稳定，尽管对于任意初始条件可能仍然存在不稳定性。
We propose a class of theories that can limit scalars constructed from the extrinsic curvature. Applied to cosmology, this framework allows us to control not only the Hubble parameter but also anisotropies without the problem of Ostrogradsky ghost, which is in sharp contrast to the case of limiting spacetime curvature scalars. Our theory can be viewed as a generalization of mimetic and cuscuton theories (thus clarifying their relation), which are known to possess a structure that limits only the Hubble parameter on homogeneous and isotropic backgrounds. As an application of our framework, we construct a model where both anisotropies and the Hubble parameter are kept finite at any stage in the evolution of the universe in the diagonal Bianchi type I setup. The universe starts from a constant-anisotropy phase and recovers Einstein gravity at low energies. We also show that the cosmological solution is stable against a wide class of perturbation wavenumbers, though instabilities may remain for arbitrary initial conditions.
