SO(10)grand unification inMtheory on aG2manifold

We consider grand unified theories based on $SO(10)$ which originate from $\text{string}/M$ theory on ${G}_{2}$ manifolds or Calabi-Yau spaces with discrete symmetries. In this framework we are naturally led to a novel solution of the doublet-triplet splitting problem previously considered by Dvali which involves an extra vectorlike Standard Model family and light but weakly coupled color triplets. These additional states are predicted to be accessible at the LHC and also induce R-parity violation. Gauge coupling unification occurs with a larger GUT coupling.