来自碎裂微团簇的瞬态轴子流
Transient axion streams from disrupted miniclusters
AI总结：
通过蒙特卡洛模拟和示踪粒子重建，研究银河系晕中恒星遭遇潮汐瓦解轴子微团簇产生的轴子流的形成与演化，发现流密度在宇宙时间尺度上可下降约10^{-9}倍，导致太阳附近稳态密度极低，观测到的流主要来自罕见近期瓦解事件，且流线宽远小于现有谐振腔实验带宽。
摘要：
我们研究了银河系晕中恒星遭遇潮汐瓦解轴子微团簇产生的轴子流的形成与演化。结合大规模蒙特卡洛处理重复恒星飞越与剥离碎片的示踪粒子重建，我们追踪了流在宽泛的银心半径范围内的相空间演化，并评估了它们对局域暗物质分布的贡献。我们发现，剥离碎片的动能通常超过其形成时的残余自引力束缚能，因此后续演化由各向异性自由膨胀和轨道剪切主导。结果，流密度在银河系时间尺度上可下降高达约10^{-9}倍，强烈抑制了太阳圈附近稠密流的稳态丰度。在太阳半径处，只有一小部分实现给出10年曝光期内非零的遭遇概率，这意味着可观测的流主要由罕见的近期和附近瓦解事件主导，而非由持久的、长寿命的稠密亚结构群体主导。尽管快速稀释，这些流仍保持动力学冷，并产生比当前谐振腔实验的腔带宽窄多个数量级的探测器框架线宽。对于典型的谐振腔配置，我们得到特征流线宽在Δν_{\rm stream}\sim10^{-7}-10^{1}\,{\rm Hz}范围内，而相应的多普勒漂移远低于腔响应宽度。
英文摘要：
We investigate the formation and evolution of axion streams generated by the tidal disruption of axion miniclusters through stellar encounters in the Milky Way halo. Combining a large-scale Monte Carlo treatment of repeated stellar flybys with a tracer reconstruction of the stripped debris, we follow the phase-space evolution of the streams across a broad range of galactocentric radii and assess their contribution to the local dark matter distribution. We find that the kinetic energy of the stripped debris typically exceeds its residual self-gravitational binding energy at formation, so that the subsequent evolution is dominated by anisotropic free expansion and orbital shear. As a result, stream densities can decrease by factors as large as $\sim10^{-9}$ over Galactic timescales, strongly suppressing the steady-state abundance of dense streams near the Solar circle. At the Solar radius, only a small fraction of realizations yields a nonzero encounter probability over a 10-year exposure, implying that observable streams are dominated by rare recent and nearby disruption events rather than by a persistent population of long-lived overdense substructure. Despite this rapid dilution, the streams remain dynamically cold and produce detector-frame linewidths many orders of magnitude narrower than the cavity bandwidths of current haloscope experiments. For representative haloscope configurations, we find characteristic stream linewidths in the range $Δν_{\rm stream}\sim10^{-7}\mathrm{-}10^{1}\,{\rm Hz}$, while the corresponding Doppler drift remains well below the cavity response width.
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