标题： 第四代马约拉纳中微子、暗物质与希格斯物理 显示英文标题

标题： Fourth generation Majorana neutrino, dark matter and Higgs physics

摘要： 我们考虑了标准模型扩展（SM4）中包含第四代费米子的情况，并引入额外的对称性，使得第四代费米子与前三代费米子之间的跃迁被禁止。在这些模型中，来自直接搜索的第四代夸克质量的严格下限得以放松，同时允许最轻的第四代中微子是稳定的且足够轻以触发希格斯玻色子的不可见衰变。此外，第四代马约拉纳中微子可以成为次主导但高度可探测的暗物质组分。我们对这类SM4模型下LHC当前数据中的希格斯产生和衰变进行了全局分析。结果显示，最轻的第四代马约拉纳中微子的质量限制在$\sim 41-59$GeV 范围内。在允许的参数空间内，自旋无关暗物质-原子核散射的有效截面预测值为$\sim 3\times 10^{-48}-6\times 10^{-46} \text{cm}^{2}$，接近当前Xenon100的上限，并且在未来即将进行的Xenon1T实验中可以达到。预测的自旋相关截面也可以达到$\sim 8\times 10^{-40}\text{cm}^{2}$。 显示英文摘要

摘要： We consider extensions of the standard model with fourth generation fermions (SM4) in which extra symmetries are introduced such that the transitions between the fourth generation fermions and the ones in the first three generations are forbidden. In these models, the stringent lower bounds on the masses of fourth generation quarks from direct searches are relaxed, and the lightest fourth neutrino is allowed to be stable and light enough to trigger the Higgs boson invisible decay. In addition, the fourth Majorana neutrino can be a subdominant but highly detectable dark matter component. We perform a global analysis of the current LHC data on the Higgs production and decay in this type of SM4. The results show that the mass of the lightest fourth Majorana neutrino is confined in the range $\sim 41-59$ GeV. Within the allowed parameter space, the predicted effective cross-section for spin-independent DM-nucleus scattering is $\sim 3\times 10^{-48}-6\times 10^{-46} \text{cm}^{2}$, which is close to the current Xenon100 upper limit and is within the reach of the Xenon1T experiment in the near future. The predicted spin-dependent cross sections can also reach $\sim 8\times 10^{-40}\text{cm}^{2}$.