  In order to calculate QED corrections to hadronic physical quantities by
means of lattice simulations, a coherent description of electrically-charged
states in finite volume is needed. In the usual periodic setup, Gauss's law and
large gauge transformations forbid the propagation of electrically-charged
states. A possible solution to this problem, which does not violate the axioms
of local quantum field theory, has been proposed by Wiese and Polley, and is
based on the use of C* boundary conditions. We present a thorough analysis of
the properties and symmetries of QED in isolation and QED coupled to QCD, with
C* boundary conditions. In particular we learn that a certain class of
electrically-charged states can be constructed in this setup in a fully
consistent fashion, without relying on gauge fixing. We argue that this class
of states covers most of the interesting phenomenological applications in the
framework of numerical simulations. We also calculate finite-volume corrections
to the mass of stable charged particles and show that these are much smaller
than in non-local formulations of QED.
