Signatures of hidden particles in strong external fields

随着高强度激光脉冲和其他强电磁场源的出现，从光学和原子物理学到当代物理学的其他分支出现了新的桥梁。作为一个突出的例子，我们将在这个项目中探索如何高精度的偏振和光谱技术，结合上述强场源，可以用来探测理论上预测的存在，但迄今尚未观察到的，非常弱的相互作用的粒子与低质量。其中包括所谓的轴子、准光子和微电荷，它们被认为是解决核物理和粒子物理中基本未决问题的关键，世界各地正在进行大量的实验努力来寻找这些隐藏的粒子。虽然到目前为止还没有检测到它们，但对粒子参数（如质量和电荷）的允许范围进行了限制。理论的任务是通过开发先进的方案来支持这些搜索，在这些方案中，这些假设粒子的签名可能更容易观察。目前的理论项目旨在通过探索这种隐藏的光粒子的存在会引起的各种可能的效应来为这一努力做出贡献。特别是，麦克斯韦理论的非线性量子修正应进行研究，导致在强（激光）场的存在下物理真空的光学性质的修改。此外，微小的位移的电子在原子的能级受到外部磁场将被评估。计划使用的理论技术的多样性，包括有效的行动，标准微扰理论，真空极化张量和光学theorem.The我们的研究的总目标是显着提高可达到的上限相比，最严格的限制，目前的实验室为基础的搜索建立的隐藏粒子参数。这样，通过相应的实验发现（或排除）新的基本粒子的潜力将大大提高，使强外场中的非线性光学和原子物理成为一种补充的低能途径，以解开我们宇宙中物质的基本组成部分。

With the availability of high-intensity laser pulses and other sources of strong electromagnetic fields, novel bridges currently emerge from optics and atomic physics to other branches of contemporary physics. As a striking example, we shall explore in this project how high-precision polarimetric and spectroscopic techniques, in combination with the aforementioned strong field sources, can be utilized to probe the existence of theoretically predicted, but hitherto unobserved, very weakly interacting particles with low masses. Among them are so-called axions, paraphotons and minicharges which have been put forward as central keys for solving fundamental open questions in nuclear and particles physics.Considerable experimental efforts to search for these hidden particles are being carried out worldwide. While none of them has been detected so far, constraints on the allowed range of particle parameters (such as mass and charge) have been imposed. It is the task of theory to support these searches by developing advanced schemes where signatures of these hypothetical particles might be easier to observe. The present theoretical project aims to contribute to this endeavour by exploring various plausible effects which the existence of such hidden light particles would induce. In particular, nonlinear quantum corrections to Maxwell's theory shall be studied, leading to modifications of the optical properties of the physical vacuum in the presence of a strong (laser) field. Also tiny shifts of the electronic energy levels in atoms subject to an external magnetic field will be evaluated. A diversity of theoretical techniques is planned to be used, including effective actions, standard perturbation theory, the vacuum polarization tensor and the optical theorem.The general goal of our study is to significantly improve the attainable upper limits on the hidden particle parameters as compared with the most stringent constraints established by current laboratory-based searches. This way, the potential for discovery (or exclusion) of novel fundamental particles by corresponding experiments will be enhanced substantially, rendering nonlinear optics and atomic physics in strong external fields a complementary low-energy route to unravel the basic building blocks of matter in our universe.