宇宙学中零能量密度的引力源
Gravitating sources with zero energy density in cosmology
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中文总结 AI 辅助
本文研究宇宙学中零能量密度但非零压力的引力源，构建比例压力和恒定压力背景模型，分析标量场实现及线性扰动，发现特定模型中尘埃模式增长受限，并给出Bianchi I精确解。
中文摘要 AI 辅助
宇宙学源可以具有恒等于零的共动能量密度，但仍通过其压力产生引力效应。这与能量密度在孤立时刻经过零值的情况不同。在非静态FLRW宇宙中，维持零密度与非零压力需要能量交换。我们构建了比例压力和恒定压力背景，包括稳态、反弹、再坍缩和$\Lambda$CDM膨胀历史，并将它们与产生压力、体粘度和时间相关真空描述联系起来。标量场可以沿轨迹实现零密度；将其作为恒等式强加于类时$P(X,\phi)$域上，则选择$P=A(\phi)\sqrt{X}$，对于非零$A$，局部为带符号的无势能cuscuton。我们在不除以消失的背景密度的情况下表述线性扰动。对于具有类时场梯度的非简并$P(X,\phi)$标量，当相互作用保持其主动力学结构不变时，零密度和负压力不能与正动能和梯度系数共存。两个模型通过场相关质量将标量与粒子数守恒的尘埃耦合。比例压力轨迹是均匀鞍点，在物质源的准静态亚视界近似中，其加速分支上没有增长的幂律尘埃模式。一个不同的恒定压力模型再现了$\Lambda$CDM膨胀历史，但在相同近似下，物质主导期间最初增长的尘埃模式在低红移处达到最大值然后衰减。这些限制适用于所述标量类和模型。精确的Bianchi I解展示了由各向异性应力分别守恒的零密度源。逆压力构造区分了相互作用组分的密度与可能穿越零值的推断暗能量密度。
英文摘要
A cosmological source can have identically zero comoving energy density and still gravitate through its pressure. This differs from an energy density passing through zero at an isolated time. Maintaining zero density with nonzero pressure requires energy exchange in a nonstatic FLRW universe. We construct proportional-pressure and constant-pressure backgrounds, including steady-state, bouncing, recollapsing, and $Λ$CDM expansion histories, and relate them to creation pressure, bulk viscosity, and time-dependent vacuum descriptions. Scalar fields can realize zero density along a trajectory; imposing it as an identity on a timelike $P(X,ϕ)$ domain selects $P=A(ϕ)\sqrt{X}$, locally a signed potential-free cuscuton for nonzero $A$. We formulate linear perturbations without dividing by the vanishing background density. For a nondegenerate $P(X,ϕ)$ scalar with a timelike field gradient, zero density and negative pressure cannot coexist with positive kinetic and gradient coefficients when the interaction leaves its principal kinetic structure unchanged. Two models couple the scalar to number-conserving dust through a field-dependent mass. The proportional-pressure trajectory is a homogeneous saddle and has no growing power-law dust mode on its accelerating branch in the matter-sourced quasistatic subhorizon approximation. A distinct constant-pressure model reproduces the $Λ$CDM expansion history, but in the same approximation the dust mode that initially grows during matter domination reaches a maximum at low redshift and then decays. These restrictions apply to the stated scalar class and models. Exact Bianchi I solutions demonstrate separately conserved zero-density sources supported by anisotropic stress. An inverse-pressure construction distinguishes the density of an interacting constituent from an inferred dark-energy density that may cross zero.
发表机构
- Istanbul Technical University（伊斯坦布尔技术大学）
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