相互作用的暗能量和暗物质流体中的大尺度不稳定性
On the large-scale instability in interacting dark energy and dark matter fluids
摘要：
最近，Valiviita等人（2008）报道了耦合暗能量和暗物质模型中的大尺度早期不稳定性。我们采取同样的形式的能量动量交换和专门的情况下，当相互作用率是成比例的哈勃参数和暗能量密度。对于给定的状态方程参数，只要耦合足够小，就可以避免不稳定性。在辐射和物质主导的制度，推导出超视界尺度上的非绝热模式的表达式。我们还研究了在亚视界极限的暗物质扰动的增长。我们发现，在暗能量开始占主导地位之前，耦合对结构的生长几乎没有影响。一旦宇宙开始加速，相对的暗物质密度波动不仅停止增长，就像在非耦合模型中一样，而且实际上随着宇宙的继续膨胀而衰减。
英文摘要：
Recently, Valiviita et al. (2008) have reported a large-scale early-time instability in coupled dark energy and dark matter models. We take the same form of energy-momentum exchange and specialise to the case when the interaction rate is proportional to Hubble's parameter and the dark energy density only. Provided the coupling is made small enough for a given equation of state parameter, we show that the instability can be avoided. Expressions are derived for non-adiabatic modes on super-horizon scales in both the radiation and matter dominated regimes. We also examine the growth of dark matter perturbations in the sub-horizon limit. There we find that the coupling has almost no effect upon the growth of structure before dark energy begins to dominate. Once the universe begins to accelerate, the relative dark matter density fluctuations not only cease to grow as in uncoupled models, but actually decay as the universe continues to expand.
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