Surprises from Complete Vector Portal Theories: New Insights into the
  Dark Sector and its Interplay with Higgs Physics
  We study UV complete theories where the Standard Model (SM) gauge group is
extended with a new abelian $U(1)$, and the field content is augmented by an
arbitrary number of scalar and fermion SM singlets, potentially including dark
matter (DM) candidates. Considerations such as classical and quantum gauge
invariance of the full theory and S-matrix unitarity, not applicable within a
simplified model approach, are shown to have significant phenomenological
consequences. The lack of gauge anomalies leads to compact relations among the
$U(1)$ fermion charges, and puts a lower bound on the number of dark fermions.
Contrary to naive expectations, the DM annihilation to Zh is found to be p-wave
suppressed, as hinted by perturbative unitarity of S-matrix, with dramatic
implications for DM thermal relic density and indirect searches. Within this
framework, the interplay between dark matter, new vector boson and Higgs
physics is rather natural and generic.
