The 11th GTSS
GEOMETRYTOPOLOGY SUMMER SCHOOL
İstanbul Center for Mathematical Sciences  Online (Youtube Channel)
July 1729, 2023
First Week
Second Week
Scientific Commitee
Vicente Cortés 
University of Hamburg, Germany

Anna Fino 
University of Torino, Italy 
Ljudmila Kamenova 
Stony Brook University, USA

Lei Ni 
University of California at San Diego, USA

Tommaso Pacini 
University of Torino, Italy 
Gregory Sankaran 
University of Bath, UK 
Misha Verbitsky 
IMPA, Brasil

Organizing Commitee
Craig van Coevering 
Bosphorus University

İzzet Coşkun 
University of Illinois at Chicago, USA

Mustafa Kalafat 
Rheinische FriedrichWilhelmsUniversität Bonn

Registration
Poster
Participants
Arrival
Information
The 11th GTSS will be held at the
IMBM,
İstanbul Center for Mathematical Sciences (Online)
which is established in the main (South) Campus of Boğaziçi University (Bosphorus).
There will be minicourses of introductory nature, related to the GeometryTopology research subjects.
Application
Graduate students, recent Ph.D.s and underrepresented minorities are
especially encouraged to the summer school.
Daily expenses including bed, breakfast, lunch, dinner is around 20€.
You may stay at cheap
hostels around Taksim(Nightlife) square and take the
subway to the Campus easily.
We are trying to arrange accomodation on Campus as well.
Please fill out the
Registration form
in order to attend the "Online" summer school. Registration is free but mandatory.
Airport: İstanbul Airport  IST is the closest one. Take a
bus from the airport to the 4. Levent. Then take a taxi or subway to reach to the main/south campus.
Alternatively you can use Sabiha Gökçen Airport  SAW and take a
bus from there to 4. Levent. Then take a taxi or subway to reach to the main/south campus.
Navigate the link above for more detailed arrival and venue information.
Visas: Check whether you need a visa beforehand.
Abstracts
Actionangle coordinates and Riemannian geometry on toric manifolds
In this series of lectures my goal is to use the actionangle description of toric
manifolds to discuss two problems in Kähler Geometry.
The first problem concerns the search for Einstein metrics. Toric Kähler manifolds
have given rise to several explicit examples of Einstein metrics. But since
many Kähler manifolds do not carry KählerEinstein metrics, it is natural to relax
the Kähler condition. Derdziński has obtained a construction for 4d conformally
Kähler, Einstein metrics using special extremal Kähler metrics. In some recent
joint work with G. Oliveira we set out to apply Derdziński’s results to extremal
metrics with U(2) symmetry arising from the so called Calabi ansatz. My goal in
the first 3 lectures of the series is to report on our findings.
A second problem I want to discuss is that of finding minimal Lagrangian tori.
We will see that in the realm of toric geometry, actionangle coordinates are
extremely useful in tackling the problem.
In the first lecture, I will give an overview of toric manifolds and actionangle
coordinates on them. I will describe Calabi’s ansatz in these coordinates. I will
then use this ansatz to write the first known examples of explicit extremal non
constant scalar curvature Kähler metrics on Hirzebruch surfaces. These are due to
Calabi.
In the second lecture I will discuss Derdziński’s results. I will define Bachflat
metrics and explain how to find them in our setting.
In the third lecture I will move on to explain my joint work with G. Oliveira.
In particular I will explain how to interpret the Einstein metrics arising from the
Calabi ansatz via Derdziński duality. Some of the metrics we obtain are fillings
of S3/Zm. As it turns out, these had been previously written down in different
coordinates by Page and Pope. We explain how to “cap them off”. We also discuss
the case of CP2#CP2.
In the fourth lecture I shift gears and use the actionangle setup on toric manifolds
to address a different problem in Kähler Geometry namely that of finding
minimal Lagrangian tori. I shall explain why compact toric manifolds always carry
such objects and how find them. This is joint work with G. Oliveira.
References
 Abreu, Miguel. Kähler geometry of toric manifolds in symplectic coordinates.
Eliashberg, Yakov (ed.) et al., Symplectic and contact topology:
Interactions and perspectives.
Papers of the workshop on symplectic and contact topology,
quantum cohomology,
and symplectic field theory, Montreal and Toronto, Canada, March–April 2001.
AMS. Fields Inst. Commun. 35, 124 (2003).
Available on the ArXiv at https://arxiv.org/abs/math/0004122.
 Derdzinski, Andrzej. Selfdual Kaehler manifolds and Einstein manifolds of dimension four.
Compos. Math. 49, 405433 (1983).
Available at the authors
website.
 LeBrun, Claude. Bachflat Kähler surfaces.
J. Geom. Anal. 30, No. 3, 24912514 (2020).
Available on the ArXiv at https://arxiv.org/abs/1702.03840.
 Oliveira, Gonçalo; SenaDias, Rosa. Einstein metrics from the Calabi ansatz via Derdziński duality.
Available on the ArXiv at https://arxiv.org/abs/2306.17328.
 Oliveira, Gonçalo; SenaDias, Rosa.
Minimal Lagrangian tori and actionangle coordinates.
Trans. Am. Math. Soc. 374, No. 11, 77157742 (2021).
Available on the ArXiv at https://arxiv.org/abs/2004.14697.
Topics in SKT (Strong Kähler with torsion) geometry
In this series of lectures I will introduce strong Kähler with torsion (SKT) metrics on complex manifolds, give explicit examples of compact complex manifolds admitting such structures and study their existence on special classes of manifolds. We will then discuss their relation with curvature properties.
Partial Bibliography
1. N. Egidi. Special metrics on compact complex manifolds,
Differential Geom. Appl. 14. (2001), no.3, 217234.
2. A. Fino, M. Parton, S. Salamon. Families of strong KT structures in six dimensions,
Comment. Math. Helv. 79, no. 2, 317340 (2004)
3. A. Fino, N. Tardini. Some remarks on Hermitian manifolds satisfying Kählerlike conditions,
Math. Z., 298 (1), (2021) 4968.
4. A. Fino, N. Tardini, L. Vezzoni. Pluriclosed and Strominger Kählerlike metrics compatible with abelian complex structures.
Bull. London Math. Soc. 2022, 54(5), pp. 186272.
5. A. Fino, A. Tomassini. Blowups and resolutions of strong Kähler with torsion metrics.
Adv. Math. 221 (2009), no.~3, 914935.
6. A. Fino, A. Tomassini. On blowups and cohomology of almost complex manifolds,
Diff. Geom. Appl. 30 (2012), 520529.
7. S. Ivanov, G. Papadopoulos. Vanishing theorems and string backgrounds,
Classical and Quantum Gravity, 18 (2001), no.6, 10891110.
8. D. Popovici. NonKähler Hodge Theory and Deformations of Complex Structures.
preprint book: https://www.math.univtoulouse.fr/~popovici/hodgedef.pdf
9. N. Tardini, A. Tomassini. On geometric BottChern formality and deformations,
Ann. Mat. Pura Appl. (4) 196 (2017), no.~1, 349362.
10. S. T. Yau, Q. Zhao, F. Zheng. On Strominger Kählerlike manifolds with degenerate torsion,
Trans. Am. Math. Soc. 376(5), (2023) pp. 30633085.
11. Q. Zhao, F. Zheng. Strominger connection and pluriclosed metrics,
J. für die Reine und Angew. Math. (2023) 796, 245267
12. Q. Zhao, F. Zheng. Complex nilmanifolds and Kählerlike connections,
arXiv:1904.09707 [math.DG].
Locally conformal Kähler geometry on Lie groups
During this talks I will introduce some basic definitions involved in the no
tion of locally conformal Kähler (LCK) manifolds (complex structure, symplec
tic form, Kahler metric, etc.). I’ll focus on LCK structures on solvmanifolds,
compact quotinents Γ\G, where G is a solvable Lie group, and Γ a cocompact
discrete subgroup. We will see some examples, recent result and open problem
in this topic.
References
 A. Andrada, M. Origlia. Locally conformally Kähler solvmanifolds: a
survey.
Complex Manifolds (6) (2019), 65–87.
 S. Dragomir, L. Ornea. Locally conformal Kähler geometry.
Progress in Mathematics 155, Birkhäuser Boston, 1998.
 L. Ornea. Locally conformal Kähler manifolds. A selection of results.
Lect. Notes Semin. Interdiscip. Mat. IV (2005), 121–152.
 L. Ornea, M. Verbitsky. A report on locally conformally Kähler manifolds.
in Harmonic maps and differential geometry, Contemp. Math. 542 (2011), 135–149.
Elements of complex differential geometry via applications to drug design
The goal is to give a selfcontained survey of some topics in complex differential geometry
in the simplest setting imaginable. This actually turns out to have very useful applications
in chemistry to the field of drug discovery, which I will then outline.
1: Differential forms, complex analysis, line bundles, sections, and curvature.
2: Quantisation, Theorems of Kodaira and Tian/Bouche. Applications to Chemistry and drug design.
References
1. R Berman, J Keller: Bergman Geodesics in “Complex MongeAmpere Equations and geodesics in the space of Kaehler metrics,
Lecture Notes in Math 2038, V, Guedj, Ed. SpringerVerlag 2012
2. Daniel J. Cole, Stuart J. Hall, Thomas Murphy, Rachael Pirie. Riemannian Geometry and Molecular Similarity II: Kähler Quantization
Available on the ArXiv at https://arxiv.org/abs/2301.04424.
3. G. Szekelyhidi. An introduction to Extremal Kaehler metrics, GTM, 152, AMS.
Special Hermitian Metrics on Compact Complex Manifolds
We will present several classes of possibly nonKähler special Hermitian
metrics (SKT, Hermitiansymplectic, balanced, Gauduchon, strongly Gauduchon)
on complex manifolds and the cohomologies (BottChern, Aeppli, Dolbeault,
De Rham) that are relevant in their study. We will then study these
metrics in the context of deformations of complex structures and the
Frölicher spectral sequence.
References
 J.P. Demailly. Complex Analytic and Algebraic Geometry. self published
ebook, 1997.
https://wwwfourier.ujfgrenoble.fr/~demailly/manuscripts/agbook.pdf
 D. Popovici. NonKähler Hodge Theory and Deformations of Complex
Structures. preprint book.
https://www.math.univtoulouse.fr/~popovici/hodgedef.pdf
Topics on adinvariant metrics
We will introduce adinvariant metrics on Lie algebras from an algebraic/Lie theoretical point of view, reviewing properties and constructions.
Later, we will consider the geometry of the biinvariant metric that they induce and address their (pseudo)Riemannian geometrical properties,
among which, their isometry group will be of relevance. If time permits, the existence and uniqueness of adinvariant metrics on Lie algebras will be treated.
References
 D. Conti, V. del Barco and F. A. Rossi. Uniqueness of adinvariant metrics.
To appear in Tohoku Math. J. Available on the ArXiv at
https://arxiv.org/abs/2103.16477.
 B. O'Neil. SemiRiemannian Geometry with applications to relativity.
Academic Press, 1983.
 G. Ovando. Lie algebras with adinvariant metrics, a surveyguide.
Rend. Sem. Mat. Univ. Pol. Torino, 74 (1), 243  268, 2016.
 G. Ovando and V. del Barco. Isometric actions on pseudoRiemannian nilmanifolds.
Ann. Glob. Anal. Geom. 45 (2) (2014) 95110.
Contact: s55mtasd@unibonn.de, ilaydabariss@gmail.com, berk.bozoglu@unibonn.de
Activities are supported by University of Bonn and Boğaziçi University
