体粘滞度能建立一个可行的统一暗物质模型吗？
Does Bulk Viscosity Create a Viable Unified Dark Matter Model?
摘要：
我们详细调查的可能性，一个单一的不完美的流体与体积粘度可以取代单独的暗物质和暗能量在宇宙学模型的需要。通过选择合适的模型参数，我们证明了该模型中的背景宇宙学可以高精度地模拟LCDM宇宙。然而，随着宇宙膨胀经历减速-加速过渡，这种流体中的密度扰动迅速衰减。我们表明，虽然这并没有显着影响重子物质的结构形成，它使引力势衰减迅速在后期，导致修改宇宙学观测量的预测，如CMB功率谱和弱透镜。因此，这种统一的暗物质模型很难与天文观测相一致。我们还澄清了与其他统一的暗物质模型的差异，其中流体是正压，即，p=p（rho），如（推广的）Chaubergin气体模型，并指出它们的观测困难。我们还总结了没有引入新的动力学自由度的暗扇区模型的现状，并讨论了它们存在的问题。
英文摘要：
We investigate in detail the possibility that a single imperfect fluid with bulk viscosity can replace the need for separate dark matter and dark energy in cosmological models. With suitable choices of model parameters, we show that the background cosmology in this model can mimic that of a LCDM Universe to high precision. However, as the cosmic expansion goes through the decelerating-accelerating transition, the density perturbations in this fluid are rapidly damped out. We show that,although this does not significantly affect structure formation in baryonic matter, it makes the gravitational potential decay rapidly at late times, leading to modifications in predictions of cosmological observables such as the CMB power spectrum and weak lensing. This model of unified dark matter is thus difficult to reconcile with astronomical observations. We also clarify the differences with respect to other unified dark matter models where the fluid is barotropic, i.e., p=p(rho), such as the (generalized) Chaplygin gas model, and point out their observational difficulties. We also summarize the status of dark sector models with no new dynamical degrees of freedom introduced and discuss the problems with them.
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