E10 Orbifolds
  We study Z2 orbifolds of M-theory in terms of E10. We find a simple relation between the Z2 action on E10 and the imaginary root that corresponds [hep-th/0401053] to the "twisted sector" branes. We discuss the connection between the Kac-Moody algebra DE10 and the "untwisted" sector, and we demonstrate how DE18 can describe both the untwisted and twisted sectors simultaneously. 
Jeffrey Brown, Surya Ganguli, Ori J. Ganor and Craig Helfgott