Branched covers and matrix factorizations

Abstract

Let $(S,\mathfrak{n})$ be a regular local ring and $f$ a non-zero element of ${\mathfrak{n}}^2$. A theorem due to Knörrer states that there are finitely many isomorphism classes of maximal Cohen-Macaulay $R=S/(f)$-modules if and only if the same is true for the double branched cover of $R$, that is, the hypersurface ring defined by $f+z^2$ in $S[[z]]$. We consider an analogue of this statement in the case of the hypersurface ring defined instead by $f+z^d$ for $d\ge 2$. In particular, we show that this hypersurface, which we refer to as the $d$-fold branched cover of $R$, has finite Cohen-Macaulay representation type if and only if, up to isomorphism, there are only finitely many indecomposable matrix factorizations of $f$ with $d$ factors. As a result, we give a complete list of polynomials $f$ with this property in characteristic zero. Furthermore, we show that reduced $d$-fold matrix factorizations of $f$ correspond to Ulrich modules over the $d$-fold branched cover of $R$.

17 pages, comments welcome. v2: correction to a mistake in Example 3.6 as well as other minor changes

References in corpus (2)

• Matrix factorizations with more than two factors
• Moore Matrices and Ulrich Bundles on an Elliptic Curve

Cited by in corpus (1)

• Tensor products of $d$-fold matrix factorizations