RUI: Calculation of the Positronium Hyperfine Interval

电子偶素是电子和它的反粒子正电子的结合态。因此，它形成了一种“奇异原子”，在许多方面与传统的简单原子（如氢和氦）相似，但由于其独特的组成和湮灭倾向而不同，转化为高能光子形式的纯电磁能。正电子素的许多性质，如能级差和寿命，都可以通过高精度实验获得。 正电子素的性质也可以在理论上计算到很高的精度。因此，正电子素是检验电磁束缚态物理极限的理想系统。正电子素超精细分裂-最低能量状态的自旋-1和自旋-0变体之间的间隔-是主要的兴趣，因为这种分裂的理论和实验之间存在长期的差异（大约四倍的实验不确定性）。目前的建议是计算正电子素超精细间隔到一个更高的水平。完成后，这项工作的结果将有助于解决或锐化正电子素超精细差异。这项理论工作是及时的，因为两个实验小组，总部设在加州大学，滨江和东京大学，正在开发改进的实验测量的超精细间隔。改进的实验结果和更高精度的理论相结合，将使束缚态量子电动力学（QED）成为迄今为止最严格的测试之一。该项目的一个重要方面将是在这一领域的科学调查的技术和过程的本科生合作者的培训。 整个项目涉及许多不同的部分，这将使学生的小团队的理想项目。学生将在工作的各个方面进行合作，包括计算技术和工具的开发，计算本身，在科学会议上的演讲和出版。 正电子偶素的性质将使用束缚态量子电动力学（QED）的方法在理论上进行高精度的计算，因为强弱相互作用的影响可以忽略不计。通过完成对超精细间隔的所有三个循环校正，正电子素超精细间隔的计算将达到比迄今为止更高的精度。这将需要应用有效的场论方法，特别是非相对论QED（NRQED），在三圈的顺序。完成后，这项工作的结果将有助于解决或锐化正电子素超精细差异。

Positronium is the bound state of the electron and its antiparticle, the positron. As such, it forms an "exotic atom", similar in many ways to the traditional simple atoms such as hydrogen and helium, but different because of its unique composition and because of its tendency to annihilate, transforming into pure electromagnetic energy in the form of high-energy photons. Many properties of positronium, such as energy level differences and lifetimes, are accessible to high-precision experiments. Positronium properties can also be calculated theoretically to high precision. Consequently, positronium is an ideal system for testing the limits of electromagnetic bound state physics. The positronium hyperfine splitting--the interval between the spin-1 and spin-0 variants of the lowest energy state--is of prime interest because there is a long-standing difference (of about four times the experimental uncertainty) between theory and experiment for this splitting. The current proposal is to calculate the positronium hyperfine interval to a higher level. When complete, the result of this work will help to resolve or sharpen the positronium hyperfine discrepancy. This theoretical work is timely because two experimental groups, based at the University of California, Riverside and at the University of Tokyo, are developing improved experimental measurements of the hyperfine interval. The combination of improved experimental results and higher precision theory will work together to give bound-state Quantum Electrodynamics (QED) one of its most stringent tests to date. An important aspect of this project will be the training of undergraduate student collaborators in the techniques and processes of scientific investigation in this field. The overall project involves a number of distinct parts that will make ideal projects for small teams of students. The students will cooperate in all aspects of the work including the development of calculational techniques and tools, the calculations themselves, presentation at scientific meetings, and publication. Positronium properties will be calculated theoretically to high precision using the methods of bound-state Quantum Electrodynamics (QED) because strong and weak interaction effects are negligible. The positronium hyperfine interval will be calculated to a higher level of precision than heretofore by completing all three-loop corrections to the hyperfine interval. This will require an application of effective field theory methods, specifically Non-Relativistic QED (NRQED), at the three-loop order. When complete, the result of this work will help to resolve or sharpen the positronium hyperfine discrepancy.