大于物理量的电荷对电磁质量的修正
Finite-Volume Corrections to Electromagnetic Masses for Larger-Than-Physical Electric Charges
摘要：
在QCD中，精细结构常数的数值通常导致由于电磁作用而引起的小的同位旋破缺效应。这种微小性使得从包含电磁学的格点量子色动力学计算中确定同位旋破缺变得复杂。这个问题的一个解决方案包括使用大于物理值的电荷来执行计算，并且随后外推（或内插）到精细结构常数的物理值。最近的格点量子色动力学+ QED计算的电磁质量采用这种设置的动机下，我们考虑有限体积效应所产生的使用大于物理的电荷。一个修改的功率计数方案，这是基于处理的精细结构常数大于其物理值，探索。然而，微扰QED修正的结果是令人惊讶的。在非相对论QED的框架内，多圈图表现出产生精确抵消的动量因子分解性质。我们确定，幂律有限体积效应消失在领先的两个和三个回路的顺序，以及下一个领先的两个回路的顺序。对于比物理量大的电荷，我们预期在首阶QED之外不会有明显的体积修正。
英文摘要：
The numerical value of the fine-structure constant generally leads to small isospin-breaking effects due to electromagnetism in QCD. This smallness complicates determining isospin breaking from lattice QCD computations that include electromagnetism. One solution to this problem consists of performing computations using larger-than-physical values of the electric charge, and subsequently extrapolating (or interpolating) to the physical value of the fine-structure constant. Motivated by recent lattice QCD + QED computations of electromagnetic masses employing this setup, we consider finite-volume effects arising from the use of larger-than-physical electric charges. A modified power-counting scheme, which is based on treating the fine-structure constant as larger than its physical value, is explored. Results for perturbative QED corrections, however, are surprising. Within the framework of non-relativistic QED, multi-loop diagrams exhibit a momentum factorization property that produces exact cancellations. We determine that power-law finite-volume effects vanish at the leading two- and three-loop order, as well as the next-to-leading two-loop order. For larger-than-physical charges, we consequently expect no appreciable volume corrections beyond leading-order QED.
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