Confined Charged Particles in C-periodic Volumes
Charged particles in an Abelian Coulomb phase are non-local infraparticles that are surrounded by a cloud of soft photons which extends to infinity. Gauss' law prevents the existence of charged particles in a periodic volume. In a $C$-periodic volume, which is periodic up to charge conjugation, on the other hand, charged particles can exist. This includes vortices in the $3$-d XY-model, magnetic monopoles in $4$-d $\mathrm{U}(1)$ gauge theory, as well as protons and other charged particles in QCD coupled to QED. In four dimensions non-Abelian charges are confined. Hence, in an infinite volume non-Abelian infraparticles cost an infinite amount of energy. However, in a $C$-periodic volume non-Abelian infraparticles (whose energy increases linearly with the box size) can indeed exist. Investigating these states holds the promise of deepening our understanding of confinement.