Proton Stability and Dark Matter in a Realistic String MSSM
  We demonstrate the existence of an extra nonanomalous U(1) gauge symmetry in
a three-generation Pati-Salam model constructed with intersecting D6-branes in
Type IIA string theory on a T^6/(Z_2 \times Z_2) orientifold. This extra U(1)
forbids all dimension-4, 5, and 6 operators which mediate proton decay in the
MSSM. Moreover, this results in the effective promotion of baryon and lepton
number to local gauge symmetries, which can potentially result in leptophobic
and leptophilic $Z'$ bosons observable at the LHC. Furthermore, it is not
necessary to invoke R-parity to forbid the dimension-4 operators which allow
rapid proton decay. However, R-parity may arise naturally from a spontaneously
broken U(1)_{B-L}. Assuming the presence of R-parity, we then study the direct
detection cross-sections for neutralino dark matter, including the latest
constraints from the XENON100 experiment. We find that these limits are now
within required range necessary to begin testing the model.
