Axionic excitation and vorticity in a QCD string model with anomaly inflow

Abstract A new phenomenological model (axionic QCD string) is constructed to study the topological issues of the QCD vacuum and hadron structure. It provides an alternative way of tackling the Strong CP problem, which is different from the traditional Peccei–Quinn approach. Neither new particle nor extra symmetry is introduced, and the role of the Peccei–Quinn axion is played by a quasiparticle arising from the phase of the quark condensate, dubbed as axionic excitation. The derivative of this excitation field is decomposed into a regular part and a singular part, and the latter contains vorticity from the string configuration. A hidden gauge symmetry is revealed in this decomposition and vorticity is represented by an emergent gauge field associated with anomalies. These components, together with the anomaly-inflow mechanism, complete the effective Lagrangian description for the axionic QCD string.