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Torsion freeness of symmetric powers of ideals
Authors:Alexandre B Tchernev
Institution:Department of Mathematics, University at Albany, SUNY, Albany, New York 12222
Abstract:Let $ I$ be an ideal in a Noetherian commutative ring $ R$ with unit, let $ k\ge 2$ be an integer, and let $ \alpha_k : S_k I\longrightarrow I^k$ be the canonical surjective $ R$-module homomorphism from the $ k$th symmetric power of $ I$ to the $ k$th power of $ I$. When $ \mathrm{pd}_R I\le 1$ or when $ I$ is a perfect Gorenstein ideal of grade $ 3$, we provide a necessary and sufficient condition for $ \alpha_k$ to be an isomorphism in terms of upper bounds for the minimal number of generators of the localisations of $ I$. When $ I=\mathfrak{m}$ is a maximal ideal of $ R$ we show that $ \alpha_k$ is an isomorphism if and only if $ R_{\mathfrak{m}}$ is a regular local ring. In all three cases for $ I$ our results yield that if $ \alpha_k$ is an isomorphism, then $ \alpha_t$ is also an isomorphism for each $ 1\le t\le k$.

Keywords:Torsion freeness  symmetric algebra  Rees algebra  symmetric powers
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