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Vanishing of the top local cohomology modules over Noetherian rings
Authors:Kamran Divaani-Aazar
Affiliation:(1) Department of Mathematics, Az-Zahra University, Vanak, Post Code 19834, Tehran, Iran
Abstract:Let R be a (not necessarily local) Noetherian ring and M a finitely generated R-module of finite dimension d. Let $$
mathfrak{a}
$$ be an ideal of R and $$
mathfrak{M}
$$ denote the intersection of all prime ideals $$
mathfrak{p} in Supp_R H_mathfrak{a}^d (M)
$$. It is shown that
$$
H_mathfrak{a}^d (M) simeq H_mathfrak{M}^d (M)/sumlimits_{n in mathbb{N}} {langle mathfrak{M}rangle } (0:_{H_mathfrak{M}^d (M)} mathfrak{a}^n ),
$$
where for an Artinian R-module A we put $$
langle mathfrak{M}rangle A =  cap _{n in mathbb{N}} mathfrak{M}^n 
$$ A. As a consequence, it is proved that for all ideals $$
mathfrak{a}
$$ of R, there are only finitely many non-isomorphic top local cohomology modules $$
H_mathfrak{a}^d (M)
$$ having the same support. In addition, we establish an analogue of the Lichtenbaum-Hartshorne vanishing theorem over rings that need not be local.
Keywords:Artinian modules  attached prime ideals  cohomological dimension  formally isolated  local cohomology  secondary representations
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