Below pion threshold virtual Compton scattering off the nucleon gives access to the generalized electromagnetic polarizabilities. Different theoretical results for the generalized polarizabilities have been compared. In particular, the influence of the generalized polarizabilities on the unpolarized cross section and on double polarization observables has been investigated. Predictions for thes...

The double copy of the Coulomb solution in three dimensions is a nonvacuum that can be obtained through different matter couplings. It static black hole Einstein-Maxwell theory or general relativity minimally coupled to free scalar field (with one ghost sign action both cases). We consider generalizations these couplings by paying particular attention regularity on gravity side and correspondin...