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@ -58,3 +58,24 @@ Goresky
Schottky
Calabi
Yau
Tian
Brendle
Guenancia
Biquard
Fano
anticanonical
orbifold
Eyssidieux
Guedj
Zeriahi
Kolodziej
Cho
Choi
Hein
smoothable
Datar
Fu
Delcroix
Székelyhidi
Tosatti
Chiu

130
MFO26.tex
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@ -3,6 +3,7 @@
%
% Local font definitions -- need to come first
%
\usepackage{amsthm}
\usepackage{libertine}
\usepackage[libertine]{newtxmath}
@ -20,6 +21,8 @@
\sloppy
\newtheorem*{q}{Question}
% Colours for hyperlinks
\definecolor{lightgray}{RGB}{220,220,220}
\definecolor{gray}{RGB}{180,180,180}
@ -116,14 +119,14 @@ 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. 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.
Geometers study Lagrangian fibrations over non-compact bases in the framework of
the ``$P=W$ conjecture,'' which Maulik--Shen and Hausel--Mellit--Minets--Schiffmann
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. 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}
@ -147,57 +150,78 @@ group theory with experts on Hodge theory and to explore further potential
applications of the methods from one field to problems in the other.
\subsection{Canonical metrics and Kobayashi hyperbolicity}
\subsection{Canonical Metrics and Hyperbolicity}
\subsubsection{Kähler-Einstein metrics with conic singularities and their limits}
\subsubsection{Kähler--Einstein Metrics with Conic Singularities and Their Limits}
In the proof of Donaldson-Tian-Yau conjecture -around 2015-, the Kähler-Einstein
metrics with conic singularities along a smooth divisor are playing a key role.
Since then, they have become an object of study in its own right. For example,
we currently dispose of results which are completely analog to Yaus celebrated
solution of Calabi conjecture in conic setting, by the work of S. Brendle, S.
Donaldson, H. Guenancia, Y. Rubinstein, among many others.
In the proof of the Donaldson--Tian--Yau conjecture, which Chen--Donaldson--Sun
gave in a series of papers around 2015, Kähler--Einstein metrics with conic
singularities along a smooth divisor emerged to play a vital role. Since then,
these metrics have become an object of study in their own right. The work of
Brendle, Donaldson, Guenancia, Rubinstein, and many others provides a complete
package of results that generalize Yau's celebrated solution of the Calabi
conjecture to the conic setting. Today, many exciting recent developments in
this field gravitate around the following general question.
An important number of the exciting recent developments in this field are
gravitating around the following general question: \emph{let $X$ be a projective
manifold, and let $D\subset $ be a non-singular divisor. We assume that for each
angle $0< \beta<< 1$ small enough, there exists a unique KE metric
$\omega_\beta$ with conic singularities of angle $2\pi\beta$ along $D$, i.e.
$$Ricci_{\omega_\beta}= \lambda \omega_{\beta}+ (1-\beta)[D],$$
where $\lambda$ is equal to -1 or 1. Can one extract a limit of $(\omega_\beta)$
as $\beta\to 0$, eventually after rescaling}?
\begin{q}
Let $X$ be a projective manifold, and let $D\subset $ be a non-singular
divisor. Assume that for every sufficiently small angle $0< \beta << 1$,
there exists a unique Kähler--Einstein metric $\omega_\beta$ with conic
singularities of angle $2\pi\beta$ along $D$. In other words, assume that
\[
Ricci_{\omega_\beta}= \lambda \cdot \omega_{\beta}+ (1-\beta)\cdot [D],
\quad
\text{where } \lambda \in \{ \pm 1\}.
\]
Is there a meaningful limit of $\omega_\beta$ as $\beta\to 0$, perhaps after
rescaling?
\end{q}
The series of articles by Biquard-Guenancia —2022 and 2024-- settle many
interesting and technically challenging particular casses of this question:
toroidal compactifications of ball quotients -in which the limit mentioned above
is the hyperbolic metric- and the case of a Fano manifold together with a
divisor $D$ proportional to the anticanonical class -the limit of the rescaled
metric is the Tian-Yau metric.
\smallskip
Starting with \cite{zbMATH07615186}, a series of articles by Biquard--Guenancia
settles many relevant (and technically challenging!) particular cases of this
question.
\begin{itemize}
\item If $(X,D)$ is the toroidal compactification of a ball quotient, then the
limit of the metric exists and equals the hyperbolic metric.
On the other hand, there has been increasing interest in the understanding of
Kähler-Einstein metrics on singular spaces. Perhaps one of the first result in
this direction is due to S. Kobayashi (construction of orbifold Kähler-Einstein
metrics), while a definitive existence result for a large class of singularities
was obtained by Eyssidieux-Guedj-Zeriahi by combining Yau's technique with S.
Kolodziej's $\mathcal C^0$ estimates. Recently Li-Tian-Wang extended
Chen-Donaldson-Suns solution of the Yau-Tian-Donaldson conjecture to general
$\mathbb Q$-Fano varieties. Thus, we now have several sources/motivations for
studying singular Kähler-Einstein metrics on normal varieties.
\item If $X$ is Fano and $D$ is a divisor whose class is proportional to the
anticanonical class, then the limit of the rescaled metric exists and equals
the Tian--Yau metric.
\end{itemize}
More work is ongoing, and we expect to report on substantial progress by the
time our workshop takes place.
For applications it is desirable to have control of the geometry of these
metrics near the singularities, but so far little is known in general. The
continuity of their potential has only been established very recently (beginning
of 2024) by Y.-W- Luke and Y.-J. Choi. Beyond that, the main progress in this
direction is due to Hein-Sun, who showed that near a large class of smoothable
isolated singularities that are locally isomorphic to a Calabi-Yau cone, the
singular Calabi-Yau metric must be asymptotic in a strong sense to the
Calabi-Yau cone metric. Recently an analogous result was shown by Datar-Fu-Song
in the case of isolated log canonical singularities using the bounded geometry
method, and precise asymptotics were obtained shortly after by Fu-Hein-Jiang.
Important contributions in direct connection with these topics are due to S.-K.
Chiu,T. Delcroix, H.-J. Hein, C. Li, Y. Li, S. Sun, G. Székelyhidi, V. Tosatti
and K. Zhang.
\subsubsection{Kähler--Einstein Metrics on Singular Spaces}
Motivated by progress in the Minimal Model Program, there has been increasing
interest in Kähler--Einstein metrics on singular spaces. While one of the first
results in this direction dates back to the early 1970s when Kobayashi
constructed orbifold Kähler--Einstein metrics, a definitive existence result for
a relevant class of singularities was obtained by Eyssidieux--Guedj--Zeriahi
about 15 years ago in \cite{zbMATH05859416}, by combining Yau's technique with
Kolodziej's $\mathcal C^0$ estimates. Much more recently, Li--Tian--Wang
extended Chen-Donaldson-Sun's solution of the Yau--Tian--Donaldson conjecture to
general $\mathbb Q$-Fano varieties \cite{zbMATH07382001, zbMATH07597119}.
For most applications, it is essential to control the geometry of these metrics
near the singularities. Despite the problem's obvious importance, little is
known so far. The continuity of the metric's potential has been established
quite recently in the preprint \cite{arXiv:2401.03935} of Cho--Choi. Beyond
that, the main progress in this direction is due to Hein--Sun
\cite{zbMATH06827885}, who showed that near a large class of smoothable isolated
singularities that are locally isomorphic to a Calabi-Yau cone, the singular
Calabi-Yau metric must be asymptotic in a strong sense to the Calabi-Yau cone
metric. Using the bounded geometry method, Datar--Fu--Song recently showed an
analogous result in the case of isolated log canonical singularities
\cite{zbMATH07669617}. FuHeinJiang obtained precise asymptotics shortly
after, \cite{zbMATH07782497}. Essential contributions directly connected to
these topics are due to Chiu, Delcroix, Hein, C.~Li, Y.~Li, Sun, Székelyhidi,
Tosatti, and Zhang.
\bigskip
{\color{red}\textbf --- DO NOT READ ANYTHING BELOW THIS LINE ---}
\subsubsection{Complex hyperbolicity}

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@ -1,3 +1,132 @@
@Article{zbMATH07782497,
Author = {Fu, Xin and Hein, Hans-Joachim and Jiang, Xumin},
Title = {Asymptotics of {K{\"a}hler}-{Einstein} metrics on complex hyperbolic cusps},
FJournal = {Calculus of Variations and Partial Differential Equations},
Journal = {Calc. Var. Partial Differ. Equ.},
ISSN = {0944-2669},
Volume = {63},
Number = {1},
Pages = {34},
Note = {Id/No 6},
Year = {2024},
Language = {English},
DOI = {10.1007/s00526-023-02613-4},
Keywords = {32Q20,35J96,53C55},
zbMATH = {7782497},
Zbl = {1535.32023}
}
@Article{zbMATH07669617,
Author = {Datar, Ved and Fu, Xin and Song, Jian},
Title = {K{\"a}hler-{Einstein} metrics near an isolated log-canonical singularity},
FJournal = {Journal f{\"u}r die Reine und Angewandte Mathematik},
Journal = {J. Reine Angew. Math.},
ISSN = {0075-4102},
Volume = {797},
Pages = {79--116},
Year = {2023},
Language = {English},
DOI = {10.1515/crelle-2022-0095},
Keywords = {83C75,53C21,32Q20,03C80,35B35,83C30},
zbMATH = {7669617},
Zbl = {1521.83164}
}
@Article{zbMATH06827885,
Author = {Hein, Hans-Joachim and Sun, Song},
Title = {Calabi-{Yau} manifolds with isolated conical singularities},
FJournal = {Publications Math{\'e}matiques},
Journal = {Publ. Math., Inst. Hautes {\'E}tud. Sci.},
ISSN = {0073-8301},
Volume = {126},
Pages = {73--130},
Year = {2017},
Language = {English},
DOI = {10.1007/s10240-017-0092-1},
Keywords = {32Q25,32Q20,14J32},
URL = {www.numdam.org/articles/10.1007/s10240-017-0092-1/},
zbMATH = {6827885},
Zbl = {1397.32009}
}
@misc{arXiv:2401.03935,
title={Continuity of solutions to complex Monge-Amp\`{e}re equations on compact K\"{a}hler spaces},
author={Ye-Won Luke Cho and Young-Jun Choi},
year={2024},
eprint={2401.03935},
archivePrefix={arXiv},
primaryClass={math.DG},
url={https://arxiv.org/abs/2401.03935},
}
@Article{zbMATH07597119,
Author = {Li, Chi and Tian, Gang and Wang, Feng},
Title = {The uniform version of {Yau}-{Tian}-{Donaldson} conjecture for singular {Fano} varieties},
FJournal = {Peking Mathematical Journal},
Journal = {Peking Math. J.},
ISSN = {2096-6075},
Volume = {5},
Number = {2},
Pages = {383--426},
Year = {2022},
Language = {English},
DOI = {10.1007/s42543-021-00039-5},
Keywords = {32Q20,32Q26,14J45},
zbMATH = {7597119},
Zbl = {1504.32068}
}
@Article{zbMATH07382001,
Author = {Li, Chi and Tian, Gang and Wang, Feng},
Title = {On the {Yau}-{Tian}-{Donaldson} conjecture for singular {Fano} varieties},
FJournal = {Communications on Pure and Applied Mathematics},
Journal = {Commun. Pure Appl. Math.},
ISSN = {0010-3640},
Volume = {74},
Number = {8},
Pages = {1748--1800},
Year = {2021},
Language = {English},
DOI = {10.1002/cpa.21936},
Keywords = {32Q20,14J45,53C55},
zbMATH = {7382001},
Zbl = {1484.32041}
}
@Article{zbMATH05859416,
Author = {Eyssidieux, Philippe and Guedj, Vincent and Zeriahi, Ahmed},
Title = {Singular {K{\"a}hler}-{Einstein} metrics},
FJournal = {Journal of the American Mathematical Society},
Journal = {J. Am. Math. Soc.},
ISSN = {0894-0347},
Volume = {22},
Number = {3},
Pages = {607--639},
Year = {2009},
Language = {English},
DOI = {10.1090/S0894-0347-09-00629-8},
Keywords = {32W20,32Q20,32J27,14J17},
zbMATH = {5859416},
Zbl = {1215.32017}
}
@Article{zbMATH07615186,
Author = {Biquard, Olivier and Guenancia, Henri},
Title = {Degenerating {K{\"a}hler}-{Einstein} cones, locally symmetric cusps, and the {Tian}-{Yau} metric},
FJournal = {Inventiones Mathematicae},
Journal = {Invent. Math.},
ISSN = {0020-9910},
Volume = {230},
Number = {3},
Pages = {1101--1163},
Year = {2022},
Language = {English},
DOI = {10.1007/s00222-022-01138-5},
Keywords = {32Q20,53C55,35J99},
zbMATH = {7615186},
Zbl = {1510.32057}
}
@Article{zbMATH07790946,
Author = {Llosa Isenrich, Claudio and Py, Pierre},
Title = {Subgroups of hyperbolic groups, finiteness properties and complex hyperbolic lattices},