Standard model fermions and N =8 supergravity

In a scheme originally proposed by Gell-Mann, and subsequently shown to be realized at the SU (3 )×U (1 ) stationary point of maximal gauged SO(8) supergravity by Warner and one of the present authors, the 48 spin-1/2 fermions of the theory remaining after the removal of eight Goldstinos can be identified with the 48 quarks and leptons (including right-chiral neutrinos) of the Standard model, provided one identifies the residual SU(3) with the diagonal subgroup of the color group SU (3 )_c and a family symmetry SU (3 )_f . However, there remained a systematic mismatch in the electric charges by a spurion charge of ±1/6 . We here identify the "missing" U(1) that rectifies this mismatch, and that takes a surprisingly simple, though unexpected form.