Gauging dual symmetry

The idea of gauging (i.e. making local) symmetries of a physical system is a central feature of many modern field theories. Usually, one starts with a Lagrangian for some scalar or spinor matter fields, with the Lagrangian being invariant under a global phase symmetry transformation of the matter fields. Making this global phase symmetry local results in the introduction of vector fields. The vector fields can be said to arise as a result of the gauge principle. Here we show that this chain of reasoning can be reversed: by gauging the electric-magnetic dual symmetry of a Lagrangian which originally contains only the vector gauge fields we find that it is necessary to introduce matter fields (scalar fields in our example). In this gauging of the electric-magnetic dual symmetry the traditional roles of the vector fields and the matter fields are interchanged.