Peccei-Quinn symmetry from a hidden gauge group structure

Abstract: We introduce a natural origin of the Peccei-Quinn (PQ) symmetry with a sufficiently good precision. In the standard model, the baryon number symmetry U(1)B arises accidentally due to the SU(3)_C color gauge symmetry, and it protects the proton from a decay at a sufficient level. Likewise, if there is an SU(N) gauge symmetry in the hidden sector, an accidental hidden baryon number symmetry U(1){B_H} can appear. The hidden baryon number is solely obtained by the structure of the SU(N) group. In particular, the quality of the U(1){B_H} can be arbitrarily good for an asymptotically-free theory with large enough N. The U(1){B_H} can be identified as a PQ symmetry. Using our findings, we build two types of novel composite axion models: a model where only one SU(N) gauge symmetry is required to both guarantee the quality and break the U(1)_{B_H}, and a model with SU(N)xSU(M) gauge symmetry where the exotic quarks responsible to the axion-gluon coupling do not confine into exotic hadrons through the dynamical breaking of the PQ symmetry, and have masses of TeV scales.