Topological Defects in $[SU(6)]^3 \times Z_3$
  We study topological defects arising in the Grand Unification Model $SU(6)_L\otimes SU(6)_c \otimes SU(6)_R \times Z_3$. We show that the model does not contain domain walls, while it produces massive magnetic monopoles and it may, depending on the symmetry breaking chain, give rise to the formation of strings. We also discuss their possible relation$ the origin of the highest energy cosmic rays detected. 
H. Garc\'ia-Compe\'an, A. P\'erez-Lorenzana and A. Zepeda