Echoes of the fifth dimension?
  In this article we examine the question of whether the highest energy cosmic ray primaries could be ultra relativistic magnetic monopoles. The analysis is performed within the framework of large compact dimensions and TeV scale quantum gravity. Our study indicates that while this hypothesis must be regarded as highly speculative it cannot be ruled out with present data. 
Luis A. Anchordoqui, Thomas P. McCauley, Stephen Reucroft, and John   Swain