QCD Axion From a Spontaneously Broken B-L Gauge Symmetry

In this paper, we show that the Peccei-Quinn (PQ) symmetry with a good quality can be realized in a simple $B-L$ extension of the minimal supersymmetric standard model. The PQ symmetry is a remnant of the $B-L$ gauge symmetry at the renormalizable level. Besides, the sufficient quality of the PQ symmetry is preserved by a non anomalous discrete gauged $R$-symmetry and a small gravitino mass $m_{3/2}\ll 100$GeV. A viable mass range is $m_{3/2}=\mathcal{O}(1)$eV which allows a high reheating temperature and many baryogenesis scenarios typified by the thermal leptogenesis without any astrophysical and cosmological problems. Such a light gravitino may be tested in the future 21cm line observations.