Axion model with intermediate scale fermionic dark matter

Abstract

We investigate a non-supersymmetric SO(10)×U(1)PQ axion model in which the spontaneous breaking of U(1)PQ occurs after inflation, and the axion domain wall problem is resolved by employing the Lazarides-Shafi mechanism. This requires the introduction of two fermion 10-plets, such that the surviving discrete symmetry from the explicit U(1)PQ breaking by QCD instantons is reduced from Z12 to Z4, where Z4 coincides with the center of SO(10) (more precisely Spin(10)). An unbroken Z2 subgroup of Z4 yields intermediate scale topologically stable strings, as well as a stable electroweak doublet non-thermal dark matter candidate from the fermion 10-plets with mass comparable to or somewhat smaller than the axion decay constant fa. We present an explicit realization with inflation taken into account and which also incorporates non-thermal leptogenesis. The fermion dark matter mass lies in the 3×108−1010GeV range and its contribution to the relic dark matter abundance can be comparable to that from the axion.