Zero mass limit of Kerr spacetime is a wormhole

We show that, contrary to what is usually claimed in the literature, the zero mass limit of Ken spacetime is not flat Minkowski space but a spacetime whose geometry is only locally flat. This limiting spacetime, as the KeIT spacetime itself, contains two asymptotic regions and hence cannot he topologically trivial. It also contains a curvature singularity, because the power-law singularity of the Weyl tensor vanishes in the limit hut there remains a distributional contribution of the Ricci tensor. This spacetime can he interpreted as a wormhole sourced by a negative tension ring. We also extend the discussion to similarly interpret the zero mass limit of the Kerr-(anti-)de Sitter spacetime.