Compression of finite group actions and covariant dimension, II

Let G be a finite group and phi: V -> W an equivariant polynomial map between finite dimensional G-modules. We say that phi is faithful if G acts faithfully on phi(V). The covariant dimension of G is the minimum of the dimension of <(phi(V))over bar> taken over all faithful phi. In [Hanspeter Kraft, Gerald W. Schwarz, Compression of finite group actions and covariant dimension, J. Algebra 313 (1) (2007) 268-291] we investigated covariant dimension and were able to determine it in many cases. Our techniques largely depended upon finding homogeneous faithful covariants. After publication of the paper, the junior author of this article pointed out several gaps in our proofs. Fortunately, this inspired us to find better techniques, involving multihomogeneous covariants, which have enabled us to extend and complete the results, simplify the proofs and fill the gaps of our previous work. (C) 2009 Elsevier Inc. All rights reserved.