标题： 二重引力的最小理论：构造与宇宙学 显示英文标题

标题： Minimal Theory of Bigravity: construction and cosmology

摘要： 沿着引力替代理论中的极简路径，我们构建了“双引力的极小理论”(MTBG)，这是一个两个相互作用的自旋-2场的理论，仅传播四个局部自由度，而不是通常的七个，并且允许与Hassan-Rosen双引力(HRBG)中相同的均匀和各向同性宇宙学解。 从一个传播六个局部自由度的前体理论出发，我们仔细选择额外约束以消除其中的两个，从而构建该理论。 研究MTBG的宇宙学，我们发现它容纳了两种不同的均匀和各向同性背景解，在物理上等价于HRBG中存在的两种分支。 然而，MTBG中的这些分支在微扰水平上与HRBG的不同，两者都完全健康，既不表现出强耦合问题，也不出现鬼魅不稳定性。 在所谓的自加速分支中，该分支由有效宇宙学常数的存在所表征，标量和矢量部分与广义相对论(GR)中的一样。 在所谓的正常分支中，标量部分表现出非平凡的物理现象，而其矢量部分则与GR中的一样。 在两个分支中，张量部分表现出通常的HRBG特征：有效的质量项和引力子的振荡。 因此，MTBG为HRBG中的宇宙学提供了一个稳定的非线性完成。 显示英文摘要

摘要： Following the path of minimalism in alternative theories of gravity, we construct the "Minimal Theory of Bigravity" (MTBG), a theory of two interacting spin-2 fields that propagates only four local degrees of freedom instead of the usual seven ones and that allows for the same homogeneous and isotropic cosmological solutions as in Hassan-Rosen bigravity (HRBG). Starting from a precursor theory that propagates six local degrees of freedom, we carefully choose additional constraints to eliminate two of them to construct the theory. Investigating the cosmology of MTBG, we find that it accommodates two different branches of homogeneous and isotropic background solutions, equivalent on-shell to the two branches that are present in HRBG. Those branches in MTBG differ however from the HRBG ones at the perturbative level, are both perfectly healthy and do not exhibit strong coupling issues nor ghost instabilities. In the so-called self-accelerating branch, characterized by the presence of an effective cosmological constant, the scalar and vector sectors are the same as in General Relativity (GR). In the so-called normal branch, the scalar sector exhibits non-trivial phenomenology, while its vector sector remains the same as in GR. In both branches, the tensor sector exhibits the usual HRBG features: an effective mass term and oscillations of the gravitons. Therefore MTBG provides a stable nonlinear completion of the cosmology in HRBG.