Mathematics – Commutative Algebra
Scientific paper
2006-08-31
Adv. Math. 223 (2010) 1731--1781
Mathematics
Commutative Algebra
This version corrects an error in the statement (and proof) of Theorem 7.4 in the published version of the paper [Adv. Math. 2
Scientific paper
It is proved that the sum of the Loewy lengths of the homology modules of a finite free complex F over a local ring R is bounded below by a number depending only on R. This result uncovers, in the structure of modules of finite projective dimension, obstructions to realizing R as a closed fiber of some flat local homomorphism. Other applications include, as special cases, uniform proofs of known results on free actions of elementary abelian groups and of tori on finite CW complexes. The arguments use numerical invariants of objects in general triangulated categories, introduced here and called levels. They allow one to track, through changes of triangulated categories, homological invariants like projective dimension, as well as structural invariants like Loewy length. An intermediate result sharpens, with a new proof, the New Intersection Theorem for commutative algebras over fields. Under additional hypotheses on the ring $R$ stronger estimates are proved for Loewy lengths of modules of finite projective dimension.
Avramov Luchezar L.
Buchweitz Ragnar-Olaf
Iyengar Srikanth B.
Miller Chris
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