  Given a Haag-Kastler net on a globally hyperbolic spacetime, one can consider
a family of regions where quantum charges are supposed to be localized.
Assuming that the net fulfils certain minimal properties (factoriality of the
global observable algebra and relative Haag duality), we give a geometric
criterion that the given family must fulfil to have a superselection structure
with charges localized on its regions. Our criterion is fulfilled by all the
families used in the theory of sectors (double cones, spacelike cones,
diamonds, hypercones). In order to take account of eventual spacetime
symmetries, our superselection structures are constructed in terms of covariant
charge transporters, a novel cohomological approach generalizing that
introduced by J.E. Roberts. In the case of hypercones, with the forward light
cone as an ambient spacetime, we obtain a superselection structure with
Bose-Fermi parastatistics and particle-antiparticle conjugation.
  It could constitute a candidate for a different description of the charged
sectors introduced by Buchholz and Roberts for theories including massless
particles.
