Unification of the Standard Model and Dark Matter Sectors in
  [SU(5)$\times$U(1)]$^4$
  A simple model of dark matter contains a light Dirac field charged under a
hidden U(1) gauge symmetry. When a chiral matter content in a strong dynamics
satisfies the t'Hooft anomaly matching condition, a massless baryon is a
natural candidate of the light Dirac field. One realization is the same matter
content as the standard SU(5)$\times$U(1)$_{(B-L)}$ grand unified theory. We
propose a chiral [SU(5)$\times$U(1)]$^4$ gauge theory as a unified model of the
SM and DM sectors. The low-energy dynamics, which was recently studied, is
governed by the hidden U(1)$_4$ gauge interaction and the third-family
U(1)$_{(B-L)_3}$ gauge interaction. This model can realize self-interacting
dark matter and alleviate the small-scale crisis of collisionless cold dark
matter in the cosmological structure formation. The model can also address the
semi-leptonic $B$-decay anomaly reported by the LHCb experiment.
