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arXiv 2201.10238astro-ph.COgr-qchep-ph
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超轻轴子的精确有效流体近似

Accurate effective fluid approximation for ultralight axions

Samuel Passaglia, Wayne Hu

摘要:

超轻轴子在理论上是有趣的和现象学上丰富的暗扇区候选者,但由于它们的快速振荡,很难在宇宙学时间尺度上跟踪它们。我们通过开发一种新的方法来解决这个问题,以有效和准确地进化它们。我们首先构建一个确切的有效流体,在后期匹配的轴子,但在一个简单的方式演变。然后,我们用精心选择的状态方程和声速来近似这种演化。与我们的计划,我们发现,我们可以获得subpercent精度的线性理论抑制的轴子密度波动相对于冷暗物质,甚至没有跟踪一个完整的振荡的轴子场。我们用我们的技术来测试其他的近似方案,并提供一个拟合公式的线性理论中的物质功率谱的传递函数在轴子模型。在现有的宇宙学轴子代码中实现我们的方法是简单的,将有助于释放高精度下一代实验的潜力。

英文摘要:

Ultralight axions are theoretically interesting and phenomenologically rich dark sector candidates, but they are difficult to track across cosmological timescales because of their fast oscillations. We resolve this problem by developing a novel method to evolve them efficiently and accurately. We first construct an exact effective fluid which at late times matches the axion but which evolves in a simple way. We then approximate this evolution with a carefully chosen equation of state and sound speed. With our scheme we find that we can obtain subpercent accuracy for the linear theory suppression of axion density fluctuations relative to that of cold dark matter without tracking even a single complete oscillation of the axion field. We use our technique to test other approximation schemes and to provide a fitting formula for the transfer function for the matter power spectrum in linear theory in axion models. Implementing our approach in existing cosmological axion codes is straightforward and will help unleash the potential of high-precision next-generation experiments.

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