Automatic CP Invariance and Flavor Symmetry

Abstract

The approximate conservation of $CP$ can be naturally understood if it arises as an automatic symmetry of the renormalizable Lagrangian. We present a specific realistic example with this feature. In this example, the global Peccei-Quinn symmetry and gauge symmetries of the model make the renormalizable Lagrangian $CP$ invariant but allow non zero hierarchical masses and mixing among the three generations. The left-right and a horizontal $U(1{)}_H$ symmetry is imposed to achieve this. The non-renormalizable interactions invariant under these symmetries violate $CP$ whose magnitude can be in the experimentally required range if $U(1{)}_H$ is broken at very high, typically, near the grand unification scale.