Wormholes, Gamma Ray Bursts and the Amount of Negative Mass in the   Universe
  In this essay, we assume that negative mass objects can exist in the extragalactic space and analyze the consequences of their microlensing on light from distant Active Galactic Nuclei. We find that such events have very similar features to some observed Gamma Ray Bursts and use recent satellite data to set an upper bound to the amount of negative mass in the universe. 
Diego F. Torres, Gustavo E. Romero and Luis A. Anchordoqui