The QCD axion is investigated within the minimal supersymmetric SO(10) grand unified theory, where the Yukawa sector involves Higgs multiplets ${ \bf 10}$ and $\overline{ { \bf 126}}$. The relative phase between the VEVs of $({ \bf 10,1,3})\subset\overline{ { \bf 126}}$ and $({ \bf \overline{ 10},1,3})\subset{ \bf 126}$ under ${ \rm SU}(4)_C\times{ \rm SU}(2)_L\times{ \rm SU}(2)_R$ is identified with the axion. The Peccei-Quinn and $B-L$ symmetry breaking scales coincide through $|\langle\Delta_R\rangle|=|\langle\overline{ \Delta}_R\rangle|$. The scalar partner of the lightest right-handed neutrino plays the role of the inflaton, realizing hybrid inflation consistent with the observed CMB density fluctuations. After inflation, both fields acquire VEVs, and the domain-wall problem is resolved through the Lazarides-Shafi mechanism, which naturally restricts the model to three generations.
Categories: hep-ph
