There are two mass generating mechanisms in the standard model of particle physics (SM). One is related to the Higgs boson and fairly well understood. The other is embedded in quantum chromodynamics (QCD), the SM’s strong interaction piece; and although responsible for emergence of the roughly 1 GeV mass scale that characterises the proton and hence all observable matter, the source and impacts of this emergent hadronic mass (EHM) remain puzzling. As bound states seeded by a valence-quark and -antiquark, pseudoscalar mesons present a simpler problem in quantum field theory than that associated with the nucleon. Consequently, there is a large array of robust predictions for pion and kaon properties whose empirical validation will provide a clear window onto many effects of both mass generating mechanisms and the constructive interference between them. This has now become significant because new-era experimental facilities, in operation, construction, or planning, are capable of conducting such tests and thereby contributing greatly to resolving the puzzles of EHM. These aspects of experiment, phenomenology, and theory, along with contemporary successes and challenges, are reviewed herein. In addition to providing an overview of the experimental status, we focus on recent progress made using continuum Schwinger function methods and lattice-regularised QCD. Advances made using other theoretical tools are also sketched. Our primary goal is to highlight the potential gains that can accrue from a coherent effort aimed at finally reaching an understanding of the character and structure of Nature’s Nambu–Goldstone modes.

粒子物理标准模型 (SM) 中有两种质量生成机制。一种与希格斯玻色子有关，并且很好理解。另一个嵌入在量子色动力学（QCD）中，这是 SM 的强相互作用部分；尽管造成了表征质子和所有可观察物质的大约 1 GeV 质量尺度的出现，但这种出现的强子质量 (EHM) 的来源和影响仍然令人费解。作为价夸克和反夸克种子的束缚态，赝标量介子在量子场论中提出了比与核子相关的问题更简单的问题。最后，对 pion 和 kaon 特性有大量可靠的预测，其经验验证将为质量生成机制的许多影响以及它们之间的建设性干扰提供一个清晰的窗口。这现在变得很重要，因为在运行、建设或规划中的新时代实验设施能够进行此类测试，从而为解决 EHM 难题做出巨大贡献。本文回顾了实验、现象学和理论的这些方面，以及当代的成功和挑战。除了提供实验状态的概述外，我们还关注使用连续施温格函数方法和晶格正则化 QCD 取得的最新进展。还概述了使用其他理论工具取得的进展。