Insights into the Emergence of Mass from Studies of Pion and Kaon Structure

TL;DR

This paper reviews how studies of pion and kaon structures can shed light on the mass generation mechanisms in the Standard Model, emphasizing the role of quantum chromodynamics and recent experimental advances.

Contribution

It highlights the potential of empirical tests of meson properties to elucidate the emergent hadronic mass and the interplay of mass generation mechanisms in QCD.

Findings

Predictions for pion and kaon properties are robust and testable.

Experimental facilities are now capable of probing these meson structures.

Understanding meson structure can clarify the nature of Nambu-Goldstone modes.

Abstract

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 sketched herein, simultaneously highlighting 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.