发表机构
Centro Brasileiro de Pesquisas Físicas（巴西物理研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究在完整二次引力框架下，通过亚视界和准静态近似推导有效引力耦合及物质扰动方程，发现其通常无法重现标准宇宙学演化，仅在无极点区域可支持规则增长解，且与$f(R)$理论行为接近。
AI 中文摘要
我们研究了完整二次引力中的线性物质密度扰动。在纵向规范下，并采用亚视界和准静态近似，我们得到了该理论中有效引力耦合的代数表达式以及物质密度扰动演化的方程。我们识别了该耦合的正实极点，并描绘了它们对二次耦合的依赖关系。在形式上的红外延拓中，约化耦合恢复了其广义相对论值，而在大的物理波数下，当两个二次耦合均非零时，该耦合被抑制；单耦合极限再现了不同的行为。我们对增长模式进行了数值积分，直至第一个极点，结果表明约化系统的无极点区域可以支持规则的物质增长解，而极点则阻碍了连续的晚期演化。我们的结果表明，二次引力通常无法重现标准的宇宙学扰动演化，而在其能够重现的区域，它与$f(R)$理论的行为紧密匹配。
英文摘要
We investigate linear matter-density perturbations in full quadratic gravity. Working in the longitudinal gauge and adopting the sub-horizon and quasi-static approximations, we obtain an algebraic expression for the effective gravitational coupling in the theory and the equation for evolution of matter density perturbations. We identify the positive-real poles of this coupling and map their dependence on the quadratic couplings. In the formal infrared continuation, the reduced coupling recovers its general-relativistic value, whereas at large physical wavenumber it is suppressed when both quadratic couplings are nonzero; the single-coupling limits reproduce distinct behaviors. Numerical integrations of the growing mode are performed up to the first pole and show that pole-free regions of the reduced system can support regular matter-growth solutions, while poles obstruct a continuous late-time evolution. Our results show that quadratic gravity cannot generally reproduce the standard cosmological evolution of perturbations and in the regions where it can, it closely matches the behavior of $f(R)$ theories.
Comments8 pages, 5 figures. Submitted to PRD
