Physical states of dyons

It is shown that physical states of a non-abelian Yang-Mills-Higgs dyon are invariant under large gauge transformations that do not commute with its magnetic field. This result is established within an enlarged Hamiltonian formalism where surface terms are kept as dynamical variables. These additional variables are parameters of large gauge transformations, and are potential collective coordinates for the quantization of the monopole. Our result implies that there are no physical effects associated to some large gauge transformations and therefore their parameters should not be counted as collective coordinates.