论文标题
$ f（ϕ，{\ cal g}）$重力的宇宙稳定性
Cosmological stability in $f(ϕ,{\cal G})$ gravity
论文作者
论文摘要
In gravitational theories where a canonical scalar field $ϕ$ with a potential $V(ϕ)$ is coupled to a Gauss-Bonnet (GB) term ${\cal G}$ with the Lagrangian $f(ϕ,{\cal G})$, we study the cosmological stability of tensor and scalar perturbations in the presence of a perfect fluid.我们表明，在以积极的张量传播速度平方的减速时期，$ {\ cal g} $的非线性函数在$ f $中的存在总是会引起与GB期限相关的动力标量扰动的Laplacian不稳定。对于$ f（{\ cal g}）$重力也是这种情况，其中非线性GB函数的存在$ f（{\ cal g}）$在辐射和物质主导的时期内不允许。线性耦合的GB项，带有$ $ξ（ϕ）{\ cal g} $的$ ϕ $，只要标量GB耦合与背景宇宙学动力学相比，只要标量GB耦合与所有稳定性条件保持一致。
In gravitational theories where a canonical scalar field $ϕ$ with a potential $V(ϕ)$ is coupled to a Gauss-Bonnet (GB) term ${\cal G}$ with the Lagrangian $f(ϕ,{\cal G})$, 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 ${\cal G}$ in $f$ always induces Laplacian instability of a dynamical scalar perturbation associated with the GB term. This is also the case for $f({\cal G})$ gravity, where the presence of nonlinear GB functions $f({\cal G})$ is not allowed during the radiation- and matter-dominated epochs. A linearly coupled GB term with $ϕ$ of the form $ξ(ϕ){\cal G}$ can be consistent with all the stability conditions, provided that the scalar-GB coupling is subdominant to the background cosmological dynamics.
