Abstract: We study Kakutani equivalence in the class of unipotent flows acting on finite volume quotients of semisimple Lie groups. For every such flow we compute the Kakutani invariant of M. Ratner, the value of which being explicitly given by the Jordan block structure of the unipotent element generating the flow. This in particular answers a question of M. Ratner. Moreover it follows that the only standard unipotent flows are given by the action of (1 t ; 0 1) x id acting on SL(2,R)xG'/F where F is an irreducible lattice in SL(2,R)xG' (with the possibility that G'={e}). 


This is a joint work with Adam Kanigowski and Kurt Vinhage.


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