Duality Symmetric Electrodynamics in Curved Spacetime

We derive Maxwell equations for electric and magnetic fields in curved spacetime from first principles, relaxing an unnecessary assumption on the structure of the four-potential inherent to the standard approach and thus restoring the full consistency with the equivalence principle in the following two important cases: first, if the electromagnetic field is considered as a physical entity separate from the charged particles used to measure it, and second, if hypothetical magnetically charged particles are allowed to exist. We find that in a generic curved spacetime, the electromagnetic field has to be described by two pairs of electric and magnetic fields, instead of the only one pair which is enough in the flat spacetime case.