Cosmological stability in f(phi,G) gravity
Cosmological stability in f(phi,G) gravity
复制标题
f(phi,G) 引力中的宇宙学稳定性
DOI：
10.1016/j.physletb.2023.137751
复制
发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Shinji Tsujikawa
中科院分区：
文献类型：
--
作者：
Ryodai Kawaguchi;Shinji Tsujikawa;Shinji Tsujikawa
在引力理论中，具有势能V （φ）的正则标量场φ与具有拉格朗日量f （φ， G）的高斯-博内（GB）项G耦合，我们研究了完美流体存在下张量和标量微扰的宇宙学稳定性。我们证明，在具有正张量传播速度平方的减速宇宙时代中，G在f中的非线性函数的存在总是引起与GB项相关的动态标量扰动的拉普拉斯不稳定性。这也是f (G)引力的情况，其中非线性GB函数f (G)的存在在辐射和物质主导的时期是不允许的。如果标量-GB耦合次于背景宇宙动力学，则具有ξ （ϕ） G形式的线性耦合GB项可以与所有稳定性条件相一致。
In gravitational theories where a canonical scalar field ϕ with a potential V (ϕ) is coupled to a Gauss-Bonnet (GB) term G with the Lagrangian f (ϕ, G), we study the cosmological stability of tensor and scalar perturbations in the presence of a perfect fluid. We show that, in decelerating cosmological epochs with a positive tensor propagation speed squared, the existence of nonlinear functions of G in f always induces Laplacian instability of a dynamical scalar perturbation associated with the GB term. This is also the case for f (G) gravity, where the presence of nonlinear GB functions f (G) is not allowed during the radiation-and matter-dominated epochs. A linearly coupled GB term with ϕ of the form ξ (ϕ) G can be consistent with all the stability conditions, provided that the scalar-GB coupling is subdominant to the background cosmological dynamics.