Massless black holes and charged wormholes in string theory
  We discuss the zero mass pointlike solutions and charged Einstein-Rosen bridges (wormholes) that arise from the dyonic black hole solution of the Einstein-Maxwell-dilaton theory. These massless black holes exist individually in spacetime, different from the known massless solutions, which come in pairs with opposite signs for their masses. In order to construct a massless object, we choose the integration constants of the solution to have specific values. The massless solutions present some problems: in one case the dilaton field is complex (or the gauge field has negative kinetic energy), and in the other case the solution has negative entropy and temperature or it is naked singularity in the extremal limit. For the first case, the observables computed are real quantities. This massless solution also allow the bridge construction, and we obtain an analytical and static charged wormhole solution, which satisfies the null energy condition. 
Prieslei Goulart
hep-th gr-qc