Polarization effects in modified versions of the QED vacuum

探索量子真空是深入和清晰地理解自然基本定律的核心。虽然经典真空只是描述了一个没有物质的区域，但量子电动力学揭示了它的特征是带电量子场的波动。这使得量子真空可以被理解为一个“虚拟”的电子-正电子对的等离子体，其行为就像一个弱非线性的电介质。因此，外部场可以使真空极化，改变其介电性质并引发多种色散和吸收现象。其中一些，如著名的原子能级兰姆位移，是公认的，可以在实验中以高精度测量。其他的，像真空双折射和真空中自发产生真实的电子-正电子对，迄今为止还没有被观测到--尽管人们为它们的实验检测付出了巨大的努力。这是由于达到由电子mass.In这个理论项目的临界尺度附近的场强的技术限制，我们计划研究类似的电子-正电子量子真空，其现象的特点是低得多的能量和场尺度的真空场景。这种量子真空出现在物理学的各个领域。它们的范围从特殊的凝聚态系统（石墨烯），其中价带中的电子表现得像低质量粒子，到粒子物理学的先进理论，预测存在非常轻的弱相互作用粒子（如轴子和微电荷）。要考虑的情况可以分为三类：（a）低维系统的量子真空;（B）涉及假设光粒子波动的量子真空;（c）存在外场的量子真空。相应的极化效应发生在能量尺度上，可以用目前可用的高精度技术，如原子光谱学，偏振测量和电压测量进行实验探测。(1)我们希望利用实验验证的真空极化效应，如兰姆位移和光子分裂，探测新的粒子候选者。从在这些实验中取得的灵敏度，以及在卡文迪什一样的设置，严格的界限上的参数空间的轴子粒子和微电荷将推断。(2)关于迄今未观察到的效应（如真空双折射或真空衰减成对），我们将研究具有密切相关性质的系统中的类比，并探索放大这些效应的新方法。将使用广泛的技术，包括维紧化，重整化，量子动力学方程和微扰理论。我们的研究将揭示不同类别的量子真空之间的相互关系，并显着推进我们对各种尚未观察到的真空极化现象的理解。

Exploring the quantum vacuum is central to obtain an in-depth and clear understanding of the fundamental laws of nature. While the classical vacuum simply describes a region devoid of matter, quantum electrodynamics reveals that it is characterized by fluctuations of charged quantum fields. This allows the quantum vacuum to be understood as a plasma of "virtual" electron-positron pairs, which behaves like a weakly nonlinear, dielectric medium. An external field can thus polarize the vacuum, altering its dielectric properties and inducing a multitude of dispersive and absorptive phenomena. Some of them, like the famous Lamb shift of atomic energy levels, are well-established and can be measured with high accuracy in experiment. Others, like vacuum birefringence and the spontaneous production of real electron-positron pairs from the vacuum, have so far eluded observation - in spite of strong efforts towards their experimental detections. This is due to the technical limitations of reaching field strengths near the critical scale characterized by the electron mass.In this theoretical project, we plan to study vacuum scenarios resembling the electron-positron quantum vacuum, whose phenomenologies are characterized by much lower energy and field scales. Quantum vacua of this kind arise in various areas of physics. They range from special condensed-matter systems (graphene) where the electrons in the valence band behave like low-mass particles, to advanced theories of particle physics which predict the existence of very light, weakly interacting particles (such as axions and minicharges). The scenarios to be considered can be classified in three categories: (a) quantum vacua of low-dimensional systems; (b) quantum vacua involving fluctuations of hypothetical light particles; (c) quantum vacua in the presence of external fields. The corresponding polarization effects occur on energy scales that can be probed experimentally with currently available high-precision techniques such as atomic spectroscopy, polarimetry and voltage metering.Our aims are twofold. (1) We want to make use of experimentally verified vacuum polarization effects, such as the Lamb shift and photon splitting, to probe new particle candidates. From the sensitivities achieved in these experiments as well as in Cavendish-like setups, stringent bounds on the parameter spaces of axion-like particles and minicharges will be infered. (2) With regard to hitherto unobserved effects (such as vacuum birefringence or vacuum decay into pairs), we shall study analogies in systems with closely related properties, and explore novel ways to amplify these effects. A broad range of techniques shall be used, including dimensional compactification, renormalization, quantum kinetic equations and perturbation theory. Our studies will reveal interrelations between different classes of the quantum vacuum and significantly advance our understanding of various yet unobserved vacuum polarization phenomena.