Fresh perspectives for QED in intense backgrounds: first quantised techniques in strong field QED

强背景下 QED 的新视角：强场 QED 中的首个量化技术

• 批准号: EP/X02413X/1
• 负责人: James Edwards
• 金额: $ 30.51万
• 依托单位: Plymouth University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FX02413X%2F1
• 关键词: Fresh; perspectives; QED; intense; backgrounds

Quantum electrodynamics (QED) governs the way that light and matter interact and it is our best-tested theory of fundamental physics. Problems in QED can very often be approached, as with other physics problems, in an approximate scheme called perturbation theory. Here one performs calculations to low order in a suitably small expansion parameter, which in QED is the well-known "fine structure constant" proportional to the square of the electric charge. Going to sequentially higher orders in perturbation theory may provide higher precision results, but advances are now required in regimes of very high orders, or even all orders, to obtain meaningful theoretical insight and make sufficiently precise experimental predictions. Such a situation occurs in laser-matter interactions, and the associated higher order calculations are prohibitively challenging. Modern laser facilities create pulses of intense light with very high photon density, often focussing the equivalent of the total light emitted by the sun onto the head of a pin. The interaction of laser photons with matter adds coherently, so these great numbers of incident photons imply that the laser-matter coupling effectively becomes enhanced, from the fine-structure constant to the so-called "dimensionless intensity parameter." This parameter easily exceeds unity at current facilities - and future experiments will reach values of 10 to 100 - which clearly demands a non-perturbative treatment. Fortunately, such an approach to laser-matter interactions is made possible by the "Furry expansion," can be thought of as an improved perturbation theory that includes the effects of laser photons, thereby accounting for large values of the dimensionless intensity parameter. This is the theoretical backbone of essentially all previous, current, and future intense laser experiments.However, the Ritus-Narozhny conjecture states that as we go ever higher intensities, quantum "loop" effects, which are typically neglected even in the Furry expansion, also become enhanced by laser intensity, to such an extent that all loop orders need to be accounted for -- in effect, the Furry expansion breaks down, leaving us without our key theoretical tool. More than simply a technical or mathematical problem, the intriguing implication of the Ritus-Narozhny conjecture is that the high-intensity regime of QED is fully non-perturbative, or "strongly coupled" and therefore inaccessible to standard approximation schemes. We are therefore currently unable to give any concrete predictions for the physics of this regime, or to answer other questions on the very high intensity behaviour of QED, because non-perturbative calculations in strong fields are prohibitively difficult, at least with the standard techniques employed by the community. Understanding the physics of the high-intensity regime, and identifying "smoking gun" signals of new effects which can be searched for at future experiments, is therefore a challenge which requires new methods.Worldline techniques are highly valued in quantum field theory for their calculational efficiency, yet their usefulness in SFQED has only recently been noticed, and the take-up of such methods in the UK has been very limited. This project will develop the worldline methods required for studying QFT in electromagnetic backgrounds and apply them to strong field problems. Of particular interest is the ability, in the worldline formalism, to derive "master formulae" for whole classes of higher-order processes; this is something which is currently lacking in strong fields, but which is required if we are to understand the physics of the high-intensity regime where higher order effects become important. The project will support national diffusion of expertise in the worldline approach, to the UK and EU SFQED community, and will shed new light on perturbative and non-perturbative aspects of matter in intense laser fields.

量子电动力学（QED）控制着光和物质相互作用的方式，它是我们最好的基础物理理论。QED中的问题和其他物理问题一样，经常可以用一种叫做微扰论的近似方法来解决。在这里，我们以适当小的膨胀参数进行低阶计算，在QED中，膨胀参数是与电荷的平方成比例的众所周知的“精细结构常数”。在微扰理论中依次进入更高阶可能会提供更高精度的结果，但现在需要在非常高阶甚至所有阶的状态中取得进展，以获得有意义的理论见解并做出足够精确的实验预测。这种情况发生在激光与物质的相互作用中，相关的高阶计算是非常具有挑战性的。现代激光设备产生具有非常高光子密度的强光脉冲，通常将相当于太阳发出的总光聚焦到针尖上。激光光子与物质的相互作用相干地增加，因此这些大量的入射光子意味着激光-物质耦合有效地增强，从精细结构常数到所谓的“无量纲强度参数”。“这个参数很容易超过目前设施的单位-未来的实验将达到10至100的值-这显然需要一个非微扰处理。幸运的是，这样一种激光与物质相互作用的方法是通过“Furry expansion”来实现的，它可以被认为是一种改进的微扰理论，包括激光光子的影响，从而解释了无量纲强度参数的大值。然而，Ritus-Narozhny猜想指出，当我们达到更高的强度时，即使在Furry膨胀中通常也被忽略的量子“环”效应也会被激光强度增强，以至于所有的环阶都需要考虑--实际上，Furry膨胀会被打破，让我们失去了关键的理论工具Ritus-Narozhny猜想不仅仅是一个技术或数学问题，它有趣的含义是QED的高强度区域是完全非微扰的，或者说是“强耦合的”，因此标准近似方案无法实现。因此，我们目前无法给出任何具体的预测，这一制度的物理，或回答其他问题的非常高的强度行为的量子电动力学，因为非微扰计算在强场是非常困难的，至少与标准技术采用的社会。理解物理学的高强度制度，并确定“吸烟枪”的信号，可以在未来的实验中寻找新的效果，因此是一个挑战，需要新的methods.Worldline技术在量子场论的计算效率，高度重视，但其实用性SFQED最近才被注意到，并采取了这种方法在英国一直非常有限。本项目将开发研究电磁背景下QFT所需的世界线方法，并将其应用于强场问题。特别感兴趣的是，在世界线形式主义中，推导出高阶过程的整个类的“主公式”的能力;这是目前强场所缺乏的，但如果我们要理解高阶效应变得重要的高强度区域的物理学，这是必需的。该项目将支持在世界线方法的专业知识，英国和欧盟SFQED社区的国家传播，并将揭示在强激光场中物质的微扰和非微扰方面的新的光。

项目成果

Master formulas for N -photon tree level amplitudes in plane wave backgrounds

平面波背景中N光子树级振幅的主公式

• DOI: 10.1103/physrevd.109.065003
• 发表时间: 2024
• 期刊: Physical Review D
• 影响因子: 5
• 作者: Copinger P