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arXiv 2004.09384gr-qcastro-ph.COhep-phhep-th
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在耦合矢量张量理论中被抑制的宇宙增长

Suppressed cosmic growth in coupled vector-tensor theories

Antonio De Felice, Shintaro Nakamura, Shinji Tsujikawa

摘要:

本文研究了一个耦合暗能量的情形,在这个情形中,具有破缺$U(1)$规范对称性的大质量矢量场$A_μ$通过标积$Z=-u_c^μ A_μ$与冷暗物质的四速$u_c^μ$相互作用.这种新的耦合对应于动量传递,使得背景矢量和CDM连续性方程没有类似于能量交换的显式相互作用项。因此,非耦合广义Proca理论的观测偏好的$Λ$ CDM模型仍然可以保持在背景水平。同时,这种耦合强烈地影响着宇宙学扰动的演化。当CDM的有效声速为零时,$A_μ$的纵向标量的传播速度和无重影条件以及CDM无重影条件受到拉格朗日量中的$Z$依赖性的非平凡修改。我们提出了一个具体的暗能量模型,并表明在低红移下,与大尺度结构线性生长相关的尺度上的引力相互作用可以小于牛顿常数。这导致了CDM和总物质密度扰动的增长率的抑制,所以我们的模型允许一个有趣的可能性,减少高和低红移测量之间的物质密度对比$σ_8$的紧张局势。

英文摘要:

We study a coupled dark energy scenario in which a massive vector field $A_μ$ with broken $U(1)$ gauge symmetry interacts with the four-velocity $u_c^μ$ of cold dark matter (CDM) through the scalar product $Z=-u_c^μ A_μ$. This new coupling corresponds to the momentum transfer, so that the background vector and CDM continuity equations do not have explicit interacting terms analogous to the energy exchange. Hence the observational preference of uncoupled generalized Proca theories over the $Λ$CDM model can be still maintained at the background level. Meanwhile, the same coupling strongly affects the evolution of cosmological perturbations. While the effective sound speed of CDM vanishes, the propagation speed and no-ghost condition of a longitudinal scalar of $A_μ$ and the CDM no-ghost condition are subject to nontrivial modifications by the $Z$ dependence in the Lagrangian. We propose a concrete dark energy model and show that the gravitational interaction on scales relevant to the linear growth of large-scale structures can be smaller than the Newton constant at low redshifts. This leads to the suppression of growth rates of both CDM and total matter density perturbations, so our model allows an interesting possibility for reducing the tension of matter density contrast $σ_8$ between high- and low-redshift measurements.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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