Dark Goo：体积粘度作为暗能量的替代品
Dark goo: Bulk viscosity as an alternative to dark energy
摘要：
我们提出了一个简单的（微观）模型，其中体积粘度起着解释目前宇宙加速的作用。体积粘度对弗里德曼方程的影响是将压力转化为包含体积粘度的“有效”压力。对于足够大的体积粘度，有效压力变为负值，并且可以模拟暗能量状态方程。我们的微观模型包括自相互作用的自旋为零的粒子（体积粘度是已知的），这些粒子被添加到宇宙的通常能量含量中。我们研究了这个模型中的背景方程和线性扰动。我们表明，一个暗能量的行为得到合理的值的两个参数的模型（即质量和自旋零粒子的耦合）和线性扰动是良好的行为。没有明显的微调。我们还讨论了流体力学成立的条件，特别是自旋为零的粒子必须在局部平衡今天的粘性效应是重要的。
英文摘要：
We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an "effective" pressure containing the bulk viscosity. For a sufficiently large bulk viscosity, the effective pressure becomes negative and could mimic a dark energy equation of state. Our microscopic model includes self-interacting spin-zero particles (for which the bulk viscosity is known) that are added to the usual energy content of the universe. We study both background equations and linear perturbations in this model. We show that a dark energy behavior is obtained for reasonable values of the two parameters of the model (i.e. the mass and coupling of the spin-zero particles) and that linear perturbations are well-behaved. There is no apparent fine tuning involved. We also discuss the conditions under which hydrodynamics holds, in particular that the spin-zero particles must be in local equilibrium today for viscous effects to be important.
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