Let K be an algebraically closed field, G a linear algebraic group defined over K and V a G-module. We give upper bounds for the depth of K[V]^G, or equivalently lower bounds for the Cohen-Macaulay-Defect cmdef K[V]^G=dim K[V]^G-depth K[V]^G. So far, such bounds are only known when G is finite. In particular, we show the following result: For each reductive, but not linearly reductive group G, there exists a faithful G-module V (which we give explicitely) such that cmdef K[sum_{i=1}^{n} V]^G >= n-2 for all n.
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Let K be an algebraically closed field, G a linear algebraic group defined over K and V a G-module. We give upper bounds for the depth of K[V]^G, or equivalently lower bounds for the Cohen-Macaulay-Defect cmdef K[V]^G=dim K[V]^G-depth K[V]^G. So far, such bounds are only known when G is finite. In particular, we show the following result: For each reductive, but not linearly reductive group G, there exists a faithful G-module V (which we give explicitely) such that cmdef K[sum_{i=1}^{n} V]^G >=...
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