Cosmological perturbations for ultralight axionlike particles in a state of Bose-Einstein condensate
Cosmological perturbations for ultralight axionlike particles in a state of Bose-Einstein condensate
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玻色-爱因斯坦凝聚态超轻轴子状粒子的宇宙学扰动
DOI：
10.1103/physrevd.103.123533
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发表时间：
2021
影响因子：
5
通讯作者：
Tsujikawa Shinji
中科院分区：
文献类型：
--
作者：
Ryotaro Kase;Shinji Tsujikawa;Tsujikawa Shinji
对于像轴子这样的超轻标量粒子，暗物质可以形成具有相干经典波的玻色-爱因斯坦凝聚态（BEC），其波长为星系尺度。在有质量的振荡标量场的背景下，这种BEC描述相当于在该区域中的哈勃时间尺度上积分出场振荡。我们提供了一个规范不变的广义相对论框架研究宇宙学微扰中存在的自相互作用BEC与一个复杂的标量场。特别是，我们明确地显示从完美的流体BEC的差异，考虑到冷暗物质，重子，辐射作为一个Schutz-Sorkin描述的完美流体。我们还审查了常用的牛顿处理的准静态近似的基础上的扰动深处的哈勃半径的准确性。对于一个标量场开始振荡后，物质辐射的平等，我们表明，BEC形成后，一个负的自耦合很难导致拉普拉斯不稳定的BEC密度对比度。这是由于在非相对论BEC描述的有效性范围内，拉普拉斯不稳定性并没有压倒自相互作用的引力不稳定性。我们的分析不适应制度的参数共振，这可能会发生在一个大的字段对齐的瞬态时期之前的BEC形成。
For ultralight scalar particles like axions, dark matter can form a state of the Bose-Einstein condensate (BEC) with a coherent classical wave whose wavelength is of order galactic scales. In the context of an oscillating scalar field with mass, this BEC description amounts to integrating out the field oscillations over the Hubble timescalein the regime. We provide a gauge-invariant general relativistic framework for studying cosmological perturbations in the presence of a self-interacting BEC associated with a complex scalar field. In particular, we explicitly show the difference of BECs from perfect fluids by taking into account cold dark matter, baryons, and radiation as a Schutz-Sorkin description of perfect fluids. We also scrutinize the accuracy of commonly used Newtonian treatment based on a quasistatic approximation for perturbations deep inside the Hubble radius. For a scalar field starting to oscillate after matter-radiation equality, we show that, after the BEC formation, a negative self-coupling hardly leads to a Laplacian instability of the BEC density contrast. This is attributed to the fact that the Laplacian instability does not overwhelm the gravitational instability for self-interactions within the validity of the nonrelativistic BEC description. Our analysis does not accommodate the regime of parametric resonance, which can potentially occur for a large field alignment during the transient epoch prior to the BEC formation.