# $t$-Structures for Relative $\mathcal{D}$-Modules and $t$-Exactness of the de Rham Functor

## TL;DR

This paper investigates the behavior of $t$-structures in relative holonomic $
$-modules, revealing how duality affects $t$-exactness and establishing conditions under which key functors are $t$-exact.

## Contribution

It explicitly describes dual $t$-structures in the relative setting and proves $t$-exactness of the solution, Riemann-Hilbert, and de Rham functors in certain cases.

## Key findings

- Dual $t$-structures are explicitly characterized.
- Solution and Riemann-Hilbert functors are $t$-exact in the 1-dimensional parameter case.
- De Rham functor is $t$-exact for canonical and middle-perverse $t$-structures.

## Abstract

This paper is a contribution to the study of relative holonomic $\mathcal{D}$-modules. Contrary to the absolute case, the standard $t$-structure on holonomic $\mathcal{D}$-modules is not preserved by duality and hence the solution functor is no longer $t$-exact with respect to the canonical, resp. middle-perverse, $t$-structures. We provide an explicit description of these dual $t$-structures. When the parameter space is 1-dimensional, we use this description to prove that the solution functor as well as the relative Riemann-Hilbert functor are $t$-exact with respect to the dual $t$-structure and to the middle-perverse one while the de Rham functor is $t$-exact for the canonical, resp. middle-perverse, $t$-structures and their duals.