2024/02/06 by Yui Hayashi, Hayashi, Yui, Yuya Tanizaki +1 · 4 citations
Physics and Astronomy · #Black Holes and Theoretical Physics #FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph) #High Energy Physics - Theory (hep-th) #Nuclear Theory (nucl-th) #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2402.04320
openalex publication_date 2024/02/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We study QCD vacuum structure with the topological θ angle using a recently proposed semiclassical approach on ℝ2 × T2 with the 't Hooft and baryon magnetic fluxes. Under the assumption of adiabatic continuity in this setup, the confining vacuum can be described by the dilute gas of center vortices. With this semiclassical approach, we derive the 2d effective description at small T2 and successfully explain the reasonable theta dependence of the QCD vacuum: In the one-flavor QCD at θ= π, the CP symmetry is spontaneously broken for quark mass above a critical value and restored for a subcritical mass, while the CP symmetry is always spontaneously broken in the multi-flavor QCD at θ= π. From our semiclassical description, we discuss implications to the 4d chiral Lagrangian and propose how the η' meson should be incorporated in consistent with known global structures: The periodicity of the η' should be extended from the naive one 2π to 2πN. Additionally, we revisit the phase diagram of Nf = 1+1 and Nf = 1+1+1 QCD on the up and down quark mass plane, confirming and refining the existence of the CP-broken Dashen phase.