Trace Ideals, Normalization Chains, and Endomorphism Rings

In this paper we consider reduced (non-normal) commutative noetherian rings R.With the help of conductor ideals and trace ideals of certain R-modules we deduce a criterion for a reflexive R-module to be closed under multiplication with scalars in an integral extension of R. Using results of Greuel and Knörrer this yields a characterization of plane curves of finite Cohen–Macaulay type in terms of trace ideals.

Further, we study one-dimensional local rings (R,m) such that that their normalization is isomorphic to the endomorphism ring EndR(m): we give a criterion for this property in terms of the conductor ideal, and show that these rings are nearly Gorenstein. Moreover, using Grauert–Remmert normalization chains, we show the existence of noncommutative resolutions of singularities of low global dimensions for curve singularities.