The conductor of one-dimensional gorenstein rings in their blowing-up |
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Authors: | Ferruccio Orecchia Isabella Ramella |
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Institution: | (1) Ferruccio Orecchia and Isabella Ramella, Dipartimento di Matematica-Università di Napoli, via Mezzocannone 8-80134, Napoli, Italy |
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Abstract: | Let (A,M) be a local, one-dimensional, Cohen-Macaulay ring of multiplicity e=e(A)>1 and Hilbert function H(A). Let I=AnnA (B/A) be the conductor of A in its blowing up B. Northcott and Matlis have proved that if the embedding dimension emdim A
of A is 2 then I=Me−1 3; Corollary 13.8]. If emdim A>2 little is know about I. In 6] and 7] I is computed when the associated graded ring G(A) is reduced (in this case B in the integral closure of A). In this paper
we compute I when A is Gorenstein. There are in general upper and lower bounds for I in terms of a power of M and we start
discussing when these bounds are attained. In particular we show that in the extremal situation I=Me−1 one has emdimA=2 (thus inverting the result of Northcott and Matlis). Then we consider the case of Gorenstein rings. We prove
that if G(A) in Gorenstein then I=Mϑ where ϑ=Min{n‖H(n)=e}. If more generally A is Gorenstein then I⊂M2 or emdim A=e(A)=2. When A is the local ring of a curve at a singular point p we get, as a consequence of this last result
a proof of the following conjecture of Catanese which has interesting geometric applications 1]: if the conductor J of A in its normalization is not contained in M2 then p is a node. |
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