在 European Pulsar Timing Array 的偏振测量数据中搜寻超轻轴子暗物质的特征
Searches for signatures of ultra-light axion dark matter in polarimetry data of the European Pulsar Timing Array
AI总结：
本研究利用 EPTA 的十二颗亮线偏振脉冲星数据，结合频率学派与贝叶斯方法搜寻超轻 ALPs 暗物质诱导的单色偏振振荡，给出耦合常数限制并识别出电离层系统误差信号。
摘要：
超轻类轴子粒子（ALPs）可以成为暗物质问题的一种可行解决方案。与 ALPs 相关的标量场在与电磁场耦合时，会充当一种有源双折射介质，改变穿过其中传播的光的偏振性质。特别是，轴子场的振荡会诱发天体物理信号中线偏振辐射偏振平面的单色变化。毫秒脉冲星的射电辐射具有高线偏振比例，且其偏振性质的涨落可忽略，因此为搜寻这类表现提供了极好的工具。我们在为 European Pulsar Timing Array（EPTA）项目收集并预处理的脉冲星偏振测量数据中搜寻了 ALPs 存在的证据。我们聚焦于线偏振最亮的十二个源，同时采用频率学派和贝叶斯统计框架来搜寻来自轴子的天体物理信号。对于以 Lomb–Scargle 周期图为核心的频率学派分析，未发现具有统计显著性的信号。贝叶斯分析所使用的模型经过调整，以容纳数据中可能存在的多种确定性系统误差。在多个脉冲星的数据集中发现了一个共同频率位于 $10^{-8}$ Hz 至 $2\ imes10^{-8}$ Hz 之间的统计显著信号，该信号最有可能由地球电离层中的残余法拉第旋转解释。在 $6\ imes10^{-24}$ eV 至 $5\ imes10^{-21}$ eV 的质量范围内，我们得到了对耦合常数 $g_{aγ}$ 的严格限制，其水平与其他搜寻工作大致相当。最后，我们讨论了可能限制在脉冲星偏振测量数据中搜寻超轻轴子灵敏度的问题，以及解决这些问题的可能途径。
英文摘要：
Ultra-light axion-like particles (ALPs) can be a viable solution to the dark matter problem. The scalar field associated with ALPs, coupled to the electromagnetic field, acts as an active birefringent medium, altering the polarisation properties of light through which it propagates. In particular, oscillations of the axionic field induce monochromatic variations of the plane of linearly polarised radiation of astrophysical signals. The radio emission of millisecond pulsars provides an excellent tool to search for such manifestations, given their high fractional linear polarisation and negligible fluctuations of their polarisation properties. We have searched for the evidence of ALPs in the polarimetry measurements of pulsars collected and preprocessed for the European Pulsar Timing Array (EPTA) campaign. Focusing on the twelve brightest sources in linear polarisation, we searched for an astrophysical signal from axions using both frequentist and Bayesian statistical frameworks. For the frequentist analysis, which uses Lomb-Scargle periodograms at its core, no statistically significant signal has been found. The model used for the Bayesian analysis has been adjusted to accommodate multiple deterministic systematics that may be present in the data. A statistically significant signal has been found in the dataset of multiple pulsars with common frequency between $10^{-8}$ Hz and $2\times10^{-8}$ Hz, which can most likely be explained by the residual Faraday rotation in the terrestrial ionosphere. Strong bounds on the coupling constant $g_{aγ}$, in the same ballpark as other searches, have been obtained in the mass range between $6\times10^{-24}$ eV and $5\times10^{-21}$ eV. We conclude by discussing problems that can limit the sensitivity of our search for ultra-light axions in the polarimetry data of pulsars, and possible ways to resolve them.
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