Complex sentence: Poincaré invariance implies that only scalar combinations of field operators have non-vanishing (VEV) s. The (VEV) may break some of the internal symmetries of the Lagrangian of the field theory.
Split into simpler sentences: Poincaré invariance implies that only scalar combinations of field operators have non-vanishing VEV's. The VEV may break some of the internal symmetries of the Lagrangian of the field theory.