标题： 无歧义地测试轻子对撞机上的 positivity 显示英文标题

标题： Unambiguously Testing Positivity at Lepton Colliders

摘要： 正电子对撞机上的双光子道$e^+e^- (\mu^+\mu^-) \to \gamma \gamma$具有一个显著特征：新物理的主要贡献仅来自八维算符。 这一贡献受到一组正性界限的约束，这些界限源自量子场论的基本原理，如幺正性、局域性、解析性和洛伦兹不变性。 因此，这些正性界限适用于最直接可观测的量——双光子截面。 这种独特属性为检验这些原理提供了一个清晰、稳健且明确的方法。 我们评估了各种未来正电子对撞机探测八维算符和检验该通道正性界限的能力。 我们表明，正性界限可以消除某些有效算符中的平坦方向，并显著改变全局分析的视角。 我们还讨论了与$\gamma\gamma$过程相关的$Z\gamma/ZZ$过程的正性界限，但由于存在质量较大的$Z$玻色子，这些过程更为复杂。 显示英文摘要

摘要： The diphoton channel at lepton colliders, $e^+e^- (\mu^+\mu^-) \to \gamma \gamma$, has a remarkable feature that the leading new physics contribution comes only from dimension-eight operators. This contribution is subject to a set of positivity bounds, derived from the fundamental principles of Quantum Field Theory, such as unitarity, locality, analyticity and Lorentz invariance. These positivity bounds are thus applicable to the most direct observable -- the diphoton cross section. This unique feature provides a clear, robust, and unambiguous test of these principles. We estimate the capability of various future lepton colliders in probing the dimension-eight operators and testing the positivity bounds in this channel. We show that positivity bounds can lift certain flat directions among the effective operators and significantly change the perspectives of a global analysis. We also discuss the positivity bounds of the $Z\gamma/ZZ$ processes which are related to the $\gamma\gamma$ ones, but are more complicated due to the massive $Z$ boson.