Essential dimension of group schemes over a local scheme

In this paper we develop the theory of essential dimension of group schemes over an integral base. Shortly we concentrate over a local base. As a consequence of our theory we give a result of invariance of the essential dimension over a field. The case of group schemes over a discrete valuation ring is discussed. Moreover we propose a generalization of Ledet conjecture, which predicts the essential dimension of cyclic $p$-groups in positive characteristic, for finite commutative unipotent group schemes. And we show some results and some consequences of this new conjecture.