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\subsection{Topology of Kähler spaces: D-modules, perverse sheaves, Hodge modules}
Over the last decade, Saito's theory of Hodge modules has seen spectacular
applications in birational geometry. More recent developments connect the
theory to singularity theory, commutative algebra, and the topology of algebraic
varieties. The following topics in this area will be of particular interest to
our workshop.
applications in birational geometry. More recent developments, which are of
significant importance, connect the theory to singularity theory, commutative
algebra, and the topology of algebraic varieties. The following topics in this
area will particularly interest our workshop.
\subsubsection{Singularities and Hodge ideals}
\subsubsection{Singularities and Hodge Ideals}
In a series of influential papers starting with \cite{MR4081135}, Mustaţă and
Popa used Hodge modules to refine and generalize well-known invariants of
singularities, most notably the multiplier ideals used in analysis and algebraic
geometry. An alternative approach towards similar ends was recently suggested in
the preprint \cite{arXiv:2309.16763} of Schnell and Yang. First applications
pertain to Bernstein--Sato polynomials and their zero sets; these are important
invariants of singularities originating from commutative algebra that are hard
to compute. Schnell and Yang apply their results to conjectures of
geometry. Schnell and Yangs recent preprint \cite{arXiv:2309.16763} suggested
an alternative approach toward similar ends. The first applications pertain to
Bernstein--Sato polynomials and their zero sets; these are essential invariants
of singularities originating from commutative algebra that are hard to compute.
Schnell and Yang apply their results to conjectures of
Debarre--Casalaina-Martin--Grushevsky concerning the Riemann--Schottky problem
and the singularities of Theta divisors of principally polarized Abelian
varieties.
Very recently, Park and Popa applied perverse sheaves and D-module theory to
improve Goresky--MacPherson's classic Lefschetz theorems in the singular setting.
A program put forward by Friedman--Laza aims at understanding the Hodge
structures of degenerating Calabi--Yau varieties.
Park and Popa recently applied perverse sheaves and D-module theory to improve
Goresky--MacPherson's classic Lefschetz theorems in the singular setting. A
program put forward by Friedman--Laza aims at understanding the Hodge structures
of degenerating Calabi--Yau varieties.
\subsubsection{Lagrangian fibrations}
@ -103,41 +103,47 @@ structures of degenerating Calabi--Yau varieties.
A Lagrangian fibration of a hyperkähler manifold $M$ is a proper holomorphic map
$f : M \to B$ whose generic fibers are Langrangian.
If $M$ is compact, a well-known conjecture in the field predicts that $B$ is
projective space. In case where $B$ is smooth, the conjecture has been
established more than 16 years ago in a celebrated work of Hwang. Today, there
is new insight, as Bakker--Schnell recently found a purely Hodge theoretic proof
of Hwang's result, \cite{arXiv:2311.08977}. There is hope that these methods
give insight into the singular setting, which remains open to date.
In the non-compact setting, Lagrangian fibrations have been studied in the
framework of the so called $P=W$ conjecture, which has recently been proven by
Maulik--Shen and Hausel--Mellit--Minets--Schiffmann, \cite{arXiv:2209.02568,
arXiv:2209.05429}. In the same setting, Shen--Yin discovered a remarkable
\paragraph{Compact Setting}
If $M$ is compact, a well-known conjecture in the field predicts that $B$ is
projective space. In the case where $B$ is smooth, Hwang established the
conjecture more than 16 years ago in a celebrated paper. There is new insight
today, as Bakker--Schnell recently found a purely Hodge theoretic proof of
Hwang's result in \cite{arXiv:2311.08977}. Hopefully, these methods will give
insight into the singular setting, which remains open to date.
\paragraph{Non-compact Setting}
In the non-compact setting, geometers study Lagrangian fibrations in the
framework of the ``$P=W$ conjecture,'' which MaulikShen and
HauselMellitMinetsSchiffmann have recently proved \cite{arXiv:2209.02568,
arXiv:2209.05429}. In the same setting, ShenYin discovered a remarkable
symmetry of certain pushforward sheaves and conjectured that more general
symmetries exist. These conjectures have recently been established by Schnell,
\cite{arXiv:2303.05364}, who also proved two conjectures of Maulik--Shen--Yin on
symmetries exist. Schnell has recently established these conjectures in
\cite{arXiv:2303.05364} and also proved two conjectures of MaulikShenYin on
the behavior of certain perverse sheaves near singular fibers.
\subsubsection{Singer--Hopf conjecture and fundamental groups of Kähler manifolds}
The Singer--Hopf conjecture asserts that a closed aspherical manifold of real
The Singer-Hopf conjecture asserts that a closed aspherical manifold of real
dimension $2n$ has positive signed Euler characteristic, $(-1)^n \cdot
\chi(X)\geq 0$. This conjecture goes back to 1931, when Hopf formulated a
related version for Riemannian manifolds. Recently, Hodge-theoretic refinements
of this conjecture for Kähler manifolds have been put forward by
Arapura--Maxim--Wang, \cite{arXiv:2310.14131}. Special cases of these conjecture
have been proven, but the statement remains open in full generality.
\chi(X)\geq 0$. This conjecture goes back to 1931 when Hopf formulated a related
version for Riemannian manifolds. Recently, ArapuraMaximWang suggested
Hodge-theoretic refinements of this conjecture for Kähler manifolds in
\cite{arXiv:2310.14131}. While the methods of \cite{arXiv:2310.14131} suffice to
show particular cases, the statement remains open in full generality.
In a related direction, Llosa-Isenrich--Py found an application of complex
geometry and Hodge theory to geometric group theory, settling an old question of
Brady on finiteness properties of groups, \cite{zbMATH07790946}. As a byproduct,
the authors also obtain a proof of the classical Singer conjecture in an
important special case in the realm of Kähler manifolds.
Brady on the finiteness properties of groups \cite{zbMATH07790946}. As a
byproduct, the authors also obtain a proof of the classical Singer conjecture in
an essential particular case in the realm of Kähler manifolds.
Our goal in this workshop is to bring together several experts in geometric
group theory with experts on Hodge theory, and to explore further potential
group theory with experts on Hodge theory and to explore further potential
applications of the methods from one field to problems in the other.