Signatures of hidden particles in strong external fields

随着高强度激光脉冲和其他强电磁场来源的出现，目前出现了从光学和原子物理学到当代物理学其他分支的新桥梁。作为一个突出的例子，我们将在这个项目中探索如何利用高精度的偏振和光谱技术，与上述强场源相结合，来探测理论上预测的、但迄今未观察到的、极弱相互作用的低质量粒子的存在。其中有所谓的轴子、类光子和微型粒子，它们被提出为解决核物理和粒子物理中基本公开问题的中心钥匙。寻找这些隐藏粒子的实验工作正在世界范围内进行。虽然到目前为止还没有检测到它们，但已经对粒子参数(如质量和电荷)的允许范围施加了限制。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，这些假设粒子的特征可能更容易观察到。目前的理论项目旨在通过探索这种隐藏的轻粒子的存在将引起的各种看似合理的效应来为这一努力做出贡献。特别是，应该研究对麦克斯韦理论的非线性量子修正，从而导致在强(激光)场存在时物理真空的光学性质的改变。此外，还将评估受外部磁场影响的原子中电子能级的微小变化。我们计划使用多种理论技术，包括有效作用、标准微扰理论、真空偏振张量和光学理论。我们研究的总体目标是显著提高隐藏粒子参数的可获得上限，而不是目前基于实验室的搜索所建立的最严格的约束。这样，通过相应的实验发现(或排除)新基本粒子的可能性将大大增强，使强外场中的非线性光学和原子物理成为解开我们宇宙中物质的基本组成部分的一条补充的低能量途径。

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.