发表机构
Durham University; Institute for Particle Physics Phenomenology; Indian Institute of Science Education and Research Kolkata（杜伦大学; 粒子物理现象学研究所; 印度加尔各答科学教育与研究学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文研究 LZ 高能核反冲能否探测协同散射机制下的暗物质，发现轻暗光子可增强转换过程，使 LZ 覆盖大部分遗迹相容参数空间，直接检验决定暗物质丰度的相互作用。
AI 中文摘要
我们研究了 LZ 实验最近报道的高能核反冲事件能否探测由协同散射（即转换驱动的冻结）机制确定其遗迹丰度的暗物质（DM）。我们考虑一个与轻暗光子耦合的单态-双重态费米子暗物质模型，其中以单态为主的暗物质态与相互作用更强的双重态态之间存在约 100 keV 的质量劈裂。在小混合区域，向双重态扇区的转换成为控制遗迹丰度的瓶颈，从而实现协同散射，而同样的小混合通常会抑制直接探测。轻暗光子增强了吸热跃迁 χ1N→χ2N，使得转换驱动区域可以被高能核反冲所探测。我们发现，对于 m_A'=250 MeV，LZ 敏感区域可以覆盖几乎全部与遗迹丰度相容的参数空间，包括以转换驱动为主的区域。随着中介子质量增加，LZ 灵敏度逐渐向更大的单态-双重态混合偏移，从而减少其与协同散射区域的重叠。结合遗迹密度和反冲要求，在所考虑的中介子质量下，暗物质质量大约从 750 GeV 延伸到 1.6 TeV。因此，LZ 反冲可以直接测试主导暗物质遗迹丰度的同一相互作用和物理参数，从而在截然不同的宇宙学时代提供对同一转换机制的探测。
英文摘要
We investigate whether the high-energy nuclear recoil recently reported by LZ can probe dark matter (DM) whose relic abundance is set by coscattering, or conversion-driven freeze-out. We consider a singlet-doublet fermion DM model coupled to a light dark photon, in which the predominantly singlet-like DM state is separated from a more strongly interacting doublet-like state by a $\sim 100\,{\rm keV}$ mass splitting. In the small mixing regime, conversion into the doublet sector becomes the bottleneck controlling the relic abundance, realising coscattering, while the same small mixing would ordinarily suppress direct detection. A light dark photon enhances the endothermic transition $χ_1 N\toχ_2 N$, allowing the conversion-driven region to be probed by high-energy nuclear recoils. We find that for $m_{A'}=250~{\rm MeV}$ the LZ-sensitive region can cover essentially the full relic-compatible parameter space, including the dominantly conversion-driven regime. As the mediator mass is increased, the LZ sensitivity progressively shifts towards larger singlet-doublet mixing, reducing its overlap with the coscattering region. Combining the relic density and recoil requirements selects DM masses extending approximately from $750~{\rm GeV}$ to $1.6~{\rm TeV}$ for the mediator masses considered. The LZ recoil can therefore directly test the same interaction and physical parameters that dominantly set the DM relic abundance, providing a probe of the same conversion mechanism across vastly different cosmological epochs.
Comments18 pages, 4 figures
