Essential dimension of finite groups, by Nikita A. Karpenko and Alexander S. Merkurjev
We prove that the essential dimension of a p-group G over a
field F containing a primitive p-th root of unity is equal to
the least dimension of a faithful representation of G over F.
Nikita A. Karpenko <karpenko@math.jussieu.fr>
Alexander S. Merkurjev <merkurev@math.ucla.edu>