Hidden Symmetries, Central Charges and All That
  In this review we discuss hidden symmetries of toroidal compactifications of eleven-dimensional supergravity. We recall alternative versions of this theory which exhibit traces of the hidden symmetries when still retaining the massive Kaluza-Klein states. We reconsider them in the broader perspective of M-theory which incorporates a more extended variety of BPS states. We also argue for a new geometry that may underly these theories. All our arguments point towards an extension of the number of space-time coordinates beyond eleven. 
Bernard de Wit (Utrecht University, Utrecht, The Netherlands), Hermann   Nicolai (Albert-Einstein-Institute, Golm, Germany)