  SO(10) grand unified theories can ensure the stability of new particles in
terms of the gauge group structure itself, and in this respect are well suited
to accommodate dark matter (DM) candidates in the form of new stable massive
particles. We introduce new fermions in two vector 10 representations. When
SO(10) is broken to the standard model by a minimal 45 + 126 + 10 scalar sector
with $SU(3)_C \otimes SU(2)_L \otimes SU(2)_R\otimes U(1)_{B-L}$ as
intermediate symmetry group, the resulting lightest new states are two Dirac
fermions corresponding to combinations of the neutral members of the $SU(2)_L$
doublets in the 10's, which get splitted in mass by loop corrections involving
$W_R$. The resulting lighter mass eigenstate is stable, and has only
non-diagonal $Z_{L,R}$ neutral current couplings to the heavier neutral state.
Direct detection searches are evaded if the mass splitting is sufficiently
large to suppress kinematically inelastic light-to-heavy scatterings. By
requiring that this condition is satisfied, we obtain the upper limit $M_{W_R}
\lesssim 25$ TeV.
