Generalized nearby cycles via relative and logarithmic $\mathscr{D}$-modules

TL;DR

This paper develops a generalized theory of nearby-cycle modules for holonomic $ ext{D}$-modules on complex varieties, linking algebraic, topological, and geometric aspects through advanced $ ext{D}$-module techniques and Bernstein-Sato ideals.

Contribution

It introduces a new construction of generalized nearby-cycle modules along log strata, extending classical theories and providing a topological interpretation of Bernstein-Sato ideal zero loci.

Findings

Generalized nearby-cycle modules are constructed along log strata.

The modules relate to Sabbah's specialization complex via a relative Riemann-Hilbert correspondence.

A topological interpretation of Bernstein-Sato ideal zero loci is provided.

Abstract

For a regular map $F$ from a complex smooth affine variety $X$ to $\mathbb A^r_\mathbb C$, we construct generalized nearby-cycle modules of a regular holonomic $\mathscr D$-modules $\mathcal M$ along log strata with the log structure induced by the graph of $F$, whose relative supports are infinite unions of translated linear subvarieties of $\mathbb C^r$ determined by the zero loci of Bernstein-Sato ideals along monoid ideals. For a fixed log stratum, the nearby-cycle module corresponds to the Sabbah specialization complex of DR$(\mathcal M)$ under the relative regular Riemann-Hilbert correspondence of Fiorot-Fernandes-Sabbah, which generalizes the classical comparison theorem of Kashiwara-Malgrange for Deligne's nearby cycles. As an application, when $\mathcal M=\mathcal O_X$, we give a topological interpretation of the zero loci of Bernstein-Sato ideals of $F$ along monoid ideals under the exponential map, which answers a question of Budur-Shi-Zuo.