On the symmetry of b-functions of linear free divisors

TL;DR

This paper investigates the symmetry of roots of the b-function for linear free divisors and prehomogeneous determinants, establishing conditions under which roots are symmetric about -1 and exploring implications for Euler homogeneity.

Contribution

It proves symmetry of b-function roots for certain classes of prehomogeneous determinants and linear free divisors, extending known results and solving a posed problem.

Findings

Roots of b-functions are symmetric about -1 for reductive prehomogeneous determinants.

-1 is the only integer root of the b-function in the studied cases.

Logarithmic comparison theorem holds for Euler homogeneous Koszul free reductive linear free divisors.

Abstract

We introduce the concept of a prehomogeneous determinant as a nonreduced version of a linear free divisor. Both are special cases of prehomogeneous vector spaces. We show that the roots of the $b$-function are symmetric about -1 for reductive prehomogeneous determinants and for regular special linear free divisors. For general prehomogeneous determinants, we describe conditions under which this symmetry still holds. Combined with Kashiwara's theorem on the roots of b-functions, our symmetry result shows that -1 is the only integer root of the b-function. This gives a positive answer to a problem posed by Castro-Jimenez and Ucha-Enriquez in the above cases. We study the condition of (strong) Euler homogeneity in terms of the action of the stabilizers on the normal spaces. As an application of our results, we show that the logarithmic comparison theorem holds for Koszul free reductive linear free divisors exactly if they are (strongly) Euler homogeneous.