arXiv 1104.37972011-04astro-ph.COgr-qchep-th

零点量子涨落产生的早期暗能量

Early dark energy from zero-point quantum fluctuations

Michele Maggiore, Lukas Hollenstein, Maud Jaccard, Ermis Mitsou

备注：: 7 pages, 3 figures; v3: improved discussion, references added
发表信息：: Phys.Lett. B704 (2011) 102
DOI：: 10.1016/j.physletb.2011.09.010

摘要：

我们研究了一个宇宙学模型的暗能量密度的形式$ρ_{DE}(t)=ρ_X(t)+ρ_Z(t)$，其中$ρ_X$是加速哈勃膨胀在后期的组件和$ρ_Z(t)$是一个额外的贡献成比例的$H^2(t)$。这种形式的$ρ_Z(t)$来自于最近的一种建议，即量子场的零点涨落对总能量密度的贡献应该通过从FRW时空中计算的结果中减去闵可夫斯基空间的结果来计算。我们讨论支持这种减法的理论论据。根据定义，这消除了真空能量密度中的四次发散，而这正是宇宙学常数问题的原因。我们表明，剩余的二次发散可以被重新吸收到牛顿常数的重新定义，只有在假设的能量动量张量的真空波动是保守的隔离。然而，在超轻标量场$X$与$m_X<H_0$的存在下，作为典型的一些暗能量模型，重力有效作用量既取决于重力场，也取决于$X$场。在这种情况下，广义协方差只需要总能量-动量张量守恒，包括经典项$T^X_{μν}$和T_{μν}的真空期望值。如果这两个项之间存在能量交换，则存在潜在的可观察后果。我们构建了一个明确的模型与$ρ_X$和$ρ_Z$之间的相互作用，我们表明，总的暗能量密度$ρ_{DE}(t)=ρ_X(t)+ρ_Z(t)$始终保持在临界密度的有限分数在任何时候，提供了一个特定的早期暗能量模型。我们讨论了这一结果的巧合问题的影响，我们估计模型参数的全似然分析，使用当前的CMB，SNe Ia和BAO数据。

英文摘要：

We examine a cosmological model with a dark energy density of the form $ρ_{DE}(t)=ρ_X(t)+ρ_Z(t)$, where $ρ_X$ is the component that accelerates the Hubble expansion at late times and $ρ_Z(t)$ is an extra contribution proportional to $H^2(t)$. This form of $ρ_Z(t)$ follows from the recent proposal that the contribution of zero-point fluctuations of quantum fields to the total energy density should be computed by subtracting the Minkowski-space result from that computed in the FRW space-time. We discuss theoretical arguments that support this subtraction. By definition, this eliminates the quartic divergence in the vacuum energy density responsible for the cosmological constant problem. We show that the remaining quadratic divergence can be reabsorbed into a redefinition of Newton's constant only under the assumption that the energy-momentum tensor of vacuum fluctuations is conserved in isolation. However, in the presence of an ultra-light scalar field $X$ with $m_X<H_0$, as typical of some dark energy models, the gravity effective action depends both on the gravitational field and on the $X$ field. In this case general covariance only requires the conservation of the total energy-momentum tensor, including both the classical term $T^X_{μν}$ and the vacuum expectation value of T_{μν}. If there is an exchange of energy between these two terms, there are potentially observable consequences. We construct an explicit model with an interaction between $ρ_X$ and $ρ_Z$ and we show that the total dark energy density $ρ_{DE}(t)=ρ_X(t)+ρ_Z(t)$ always remains a finite fraction of the critical density at any time, providing a specific model of early dark energy. We discuss the implication of this result for the coincidence problem and we estimate the model parameters by means of a full likelihood analysis using current CMB, SNe Ia and BAO data.

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