Dark matter at the LHC

随着现代粒子宇宙学的出现，粒子物理学和天体物理学比以往任何时候都更加紧密地联系在一起。粒子物理学的发现对我们对宇宙的理解有直接的影响——例如，宇宙的膨胀历史在很大程度上取决于基本粒子的数量和质量。中微子质量产生的跷跷板机制与电弱理论的动力学是轻生理论的基础，它可以为观测到的宇宙重子不对称性提供解释。同样，天体物理学和宇宙学观测是研究基本粒子最灵敏的工具之一，例如，它们提供了中微子质量的最强限制。天体物理学和粒子物理学之间最受欢迎的联系是暗物质（DM）的性质。虽然它的粒子物理性质仍然未知，但有理由相信它的质量，以及与SM场耦合的任何其他新粒子的质量，都处于电弱尺度，其耦合与SM规范耦合相似。在这种情况下，通常被称为“WIMP（弱相互作用大质量粒子）奇迹”，宇宙中观测到的DM丰度可以通过热冻结来理解。对于粒子物理学来说最关键的是，这也意味着直接生产DM是在大型强子对撞机的范围内。在那里，DM的产生会以缺失横向能量的特征的形式留下线索。直接和间接DM搜索产生的许多潜在信号可能指向电弱尺度附近的DM粒子。也许这些信号中最值得注意的是来自银河系中心区域的过量伽马射线通量[11-13]，这可以用O(40 GeV) DM粒子湮灭为b夸克或轻子来解释。虽然伽马射线过量，以及文献中讨论的其他异常信号，可能是由于低估了实验或天体物理背景，但有趣的是，其中一些信号可能指向大型强子对撞机可及的DM物理。

With the advent of modern particle cosmology, particle physics and astrophysics have moved closer together than ever before. Discoveries in particle physics have direct consequences for our understanding of the cosmos - for instance, the expansion history of the Universe depends crucially on the number and masses of elementary particle species.The see-saw mechanism for neutrino mass generation, together with the dynamics of the electroweak theory, is the basis for leptogenesis, which could provide an explanation for the observed baryon asymmetry of the Universe. Similarly, astrophysical and cosmological observations are among the most sensitive tools for studying elementary particles, providing for instance the strongest limits on neutrino masses.The most widely sought-after connection between astrophysics and particle physics is the nature of dark matter (DM). While its particle physics nature is still unknown, there are reasons to believe that its mass, as well as the masses of any other new particles responsible for its coupling to SM fields, is at the electroweak scale, and its couplings are similar to the SM gauge couplings. In this scenario, often called the "WIMP (weakly interacting massive particle) miracle", the observed abundance of DM in the Universe can be understood through thermal freeze-out. Most crucially for particle physics, this would also imply that direct production of DM is within reach of the LHC. There, DM production would leave telltale traces in form of signatures with missing transverse energy.A number of potential signals from direct and indirect DM searches could point towards DM particles around the electroweak scale. Perhaps the most notable of these signals is the excess gamma ray flux from the Galactic Center region [11-13], which can be explained by annihilation of an O(40 GeV) DM particle to b quarks or leptons. While the gamma ray excess, as well as the other anomalous signals discussed in the literature, may be due to underestimated experimental or astrophysical backgrounds, it is intriguing that some of these signals could point towards DM physics within reach of the LHC.