SO(10) Models on $Z_6$\ Orbifold with Dual Wilson Line
  'Dual' is a promising key word in the particle physics at present. The string theory is dual in any sense. The observed sector and the hidden sector are dual on the 10-dim. $E_8\times E_8$ heterotic string. We find $Z_6$ orbifold models preserving the duality under a torus compactification and realizing $SO(10)$ SUSY GUT in the obserbed sector under a twist division. 
Noriyasu Ohtsubo and Masafumi Shimojo