# Trace ideals, normalization chains, and endomorphism rings

## TL;DR

This paper investigates the structure of non-normal commutative noetherian rings, characterizing certain modules and rings via trace ideals, and constructs noncommutative resolutions for curve singularities.

## Contribution

It provides new criteria for reflexive modules to be closed under scalar multiplication, characterizes finite Cohen--Macaulay type curves, and constructs low-global-dimension noncommutative resolutions.

## Key findings

- Characterization of plane curves of finite Cohen--Macaulay type
- Criterion for normalization being an endomorphism ring
- Existence of noncommutative resolutions with low global dimension

## Abstract

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 Kn\"orrer this yields a characterization of plane curves of finite Cohen--Macaulay type in terms of trace ideals. Further, we study one-dimensional local rings $(R,\mathfrak{m})$ such that that their normalization is isomorphic to the endomorphism ring $\mathrm{End}_R(\mathfrak{m})$: 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.