Contributions of two-pseudoscalar and vector-pseudoscalar meson loops to the ρ-ω mass splitting are evaluated in a covariant model based on studies of the Schwinger-Dyson equations of QCD. The role and importance of the different time orderings of the meson loops is analyzed and compared with those obtained within time-ordered perturbation theory. It is shown that each meson loop contributes less than 10% of the bare mass, and decreases as the masses of the intermediate mesons increase beyond approximately mρ/2. A mass splitting of mω − mρ ≈ 25 MeV is obtained from the ππ, KK, ωπ, ρπ, ωη, ρη and K * K channels. The model is then used to determine the effect of the two-pion loop on the ρ-meson electromagnetic form factor. It is shown that the inclusion of pion loops increases the ρ-meson charge radius by 10%.

Starting from the QCD Lagrangian and the surface tension of QCD bubbles we derive the critical size of bubbles, the nucleation probability and the nucleation site separation distance.