Bernstein–Sato varieties and annihilation of powers

Bath, Daniel

doi:10.1090/tran/8192

Bernstein–Sato varieties and annihilation of powers
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by Daniel Bath PDF

Trans. Amer. Math. Soc. 373 (2020), 8543-8582 Request permission

Abstract:

Given a complex germ $f$ near the point $\mathfrak {x}$ of the complex manifold $X$, equipped with a factorization $f = f_{1} \cdots f_{r}$, we consider the $\mathscr {D}_{X,\mathfrak {x}}[s_{1}, \dots , s_{r}]$-module generated by $F^{S} \coloneq f_{1}^{s_{1}} \cdots f_{r}^{s_{r}}$. We show for a large class of germs that the annihilator of $F^{S}$ is generated by derivations and this property does not depend on the chosen factorization of $f$.

We further study the relationship between the Bernstein–Sato variety attached to $F$ and the cohomology support loci of $f$, via the $\mathscr {D}_{X,\mathfrak {x}}$-map $\nabla _{A}$. This is related to multiplication by $f$ on certain quotient modules. We show that for our class of divisors the injectivity of $\nabla _{A}$ implies its surjectivity. Restricting to reduced, free divisors, we also show the reverse, using the theory of Lie–Rinehart algebras. In particular, we analyze the dual of $\nabla _{A}$ using techniques pioneered by Narváez–Macarro.

As an application of our results we establish a conjecture of Budur in the tame case: if $\mathrm {V}(f)$ is a central, essential, indecomposable, and tame hyperplane arrangement, then the Bernstein–Sato variety associated to $F$ contains a certain hyperplane. By the work of Budur, this verifies the Topological Mulivariable Strong Monodromy Conjecture for tame arrangements. Finally, in the reduced and free case, we characterize local systems outside the cohomology support loci of $f$ near $\mathfrak {x}$ in terms of the simplicity of modules derived from $F^{S}.$

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