Hidden flavor symmetries of SO(10) GUT
  The Yukawa interactions of the SO(10) GUT with fermions in 16-plets (as well as with singlets) have certain intrinsic ("built-in") symmetries which do not depend on the model parameters. Thus, the symmetric Yukawa interactions of the 10 and 126 dimensional Higgses have intrinsic discrete $Z_2\times Z_2$ symmetries, while the antisymmetric Yukawa interactions of the 120 dimensional Higgs have a continuous SU(2) symmetry. The couplings of SO(10) singlet fermions with fermionic 16-plets have $U(1)^3$ symmetry. We consider a possibility that some elements of these intrinsic symmetries are the residual symmetries, which originate from the (spontaneous) breaking of a larger symmetry group $G_f$. Such an embedding leads to the determination of certain elements of the relative mixing matrix $U$ between the matrices of Yukawa couplings $Y_{10}$, $Y_{126}$, $Y_{120}$, and consequently, to restrictions of masses and mixings of quarks and leptons. We explore the consequences of such embedding using the symmetry group conditions. We show how unitarity emerges from group properties and obtain the conditions it imposes on the parameters of embedding. We find that in some cases the predicted values of elements of $U$ are compatible with the existing data fits. In the supersymmetric version of SO(10) such results are renormalization group invariant. 
Borut Bajc and Alexei Yu. Smirnov
hep-ph