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Spring Semester 2026

Date / Time Speaker Title Location
18 February 2026
15:30-16:30
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Geometry Seminar

Title kein Seminar
Speaker, Affiliation
Date, Time 18 February 2026, 15:30-16:30
Location HG G 43
kein Seminar
HG G 43
25 February 2026
15:30-16:30
Details

Geometry Seminar

Title kein Seminar
Speaker, Affiliation
Date, Time 25 February 2026, 15:30-16:30
Location HG G 43
kein Seminar
HG G 43
4 March 2026
15:30-16:30 		Thomas Nikolaus
Münster
Details

Geometry Seminar

Title Singular chains as Coalgebras
Speaker, Affiliation Thomas Nikolaus, Münster
Date, Time 4 March 2026, 15:30-16:30
Location HG G 43
Abstract A very old and natural question in topology is how much information about a space X is contained in its singular homology H_*(X). It is well known that homology by itself is not a complete invariant: different spaces can have exactly the same homology groups without being homotopy equivalent. The situation becomes much more interesting once additional structure is taken into account. Instead of passing immediately to homology, one can look at the full chain complex C_*(X) together with the cross product, which is closely related to the cup product on cochains. This extra structure encodes subtle interactions between chains that are lost on homology, and it is responsible for familiar phenomena such as Massey products and Steenrod operations. In this talk, we discuss the result that singular cochains, when viewed as an E_infinity coalgebra, actually form a complete invariant of a space: the homotopy type of X can be recovered from this structure in a functorial way. This generalizes classical rational homotopy theory as well as deep results of Mandell, Yuan and Bachmann--Hahn. More generally, we explain how the result is based on a classification of "perfect" E-infinity coalgebras. All of this is joint work with F. Riedel.
Singular chains as Coalgebrasread_more
HG G 43
11 March 2026
15:30-16:30 		Marc Abboud
Université de Neuchâtel
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Geometry Seminar

Title A uniform bound on common periodic points in families of regular plane polynomial automorphisms
Speaker, Affiliation Marc Abboud, Université de Neuchâtel
Date, Time 11 March 2026, 15:30-16:30
Location HG G 43
Abstract A regular plane polynomial automorphism is a subclass of polynomial diffeomorphism f: C^2 - > C^2 of the complex affine plane with positive topological entropy. Every polynomial diffeomorphism of positive topological entropy is conjugated to a regular one. Dujardin and Favre showed that two such transformations cannot share infinitely many periodic points unless they share a common iterate. We show that this results holds uniformly in a family: Take two 1-parameter families of regular plane polynomial automorphisms (f_t) and (g_t), then there exists a constant D >0 such that for every parameter t except for a finite number of them f_t and g_t share at most D periodic points. This generalises a result of Mavraki and Schmidt who showed it for endomorphisms of the projective line. I will give a brief overview of the history of this problem and explain key tools of the proof which is based on the theory of adelic divisors and arithmetic equidistribution. This is joint work with Yugang Zhang.
A uniform bound on common periodic points in families of regular plane polynomial automorphismsread_more
HG G 43
18 March 2026
15:30-16:30 		Kathryn Hess Bellwald
EPFL
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Geometry Seminar

Title Hochschild homology: the universal shadow
Speaker, Affiliation Kathryn Hess Bellwald, EPFL
Date, Time 18 March 2026, 15:30-16:30
Location HG G 43
Abstract Hochschild homology has proved to be an important invariant in algebra and homotopy theory, in particular due to its relevance in algebraic K-theory and fixed point theory, leading to the development of numerous variants of the original construction. Ponto's theory of shadows provides a bicategorical axiomatization of Hochschild homology-type invariants, which captures the essential common properties of all known variants of Hochschild homology, such as Morita invariance. In recent work, Nima Rasekh and I clarified the relationship between shadows and Hochschild homology. After extending the notion of Hochschild homology to bicategories in a natural manner, we proved the existence of a universal shadow on any bicategory B, taking values in the Hochschild homology of B, through which all other shadows on B factor. Shadows are thus co-represented by a bicategorical version of Hochschild homology. Using the universal shadow on the free adjunction bicategory, we established a universal Morita invariance theorem, of which all known cases are immediate corollaries. In this talk I will give an overview of my work with Rasekh and provide relevant examples of shadows, including the free loop space construction, then discuss potential generalization and extensions of our results.
Hochschild homology: the universal shadowread_more
HG G 43
25 March 2026
15:30-16:30 		Cameron Rudd
University of Oxford
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Cameron Rudd, University of Oxford
Date, Time 25 March 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
8 April 2026
15:30-16:30
Details

Geometry Seminar

Title Easter break
Speaker, Affiliation
Date, Time 8 April 2026, 15:30-16:30
Location HG G 43
Easter break
HG G 43
15 April 2026
15:30-16:30 		Marc Kegel
Universidad de Sevilla
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Marc Kegel, Universidad de Sevilla
Date, Time 15 April 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
22 April 2026
15:30-16:30 		Ara Basmajian
CUNY
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Ara Basmajian, CUNY
Date, Time 22 April 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
29 April 2026
15:30-16:30 		Daniela Paiva Peñuela
Universität Basel
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Daniela Paiva Peñuela, Universität Basel
Date, Time 29 April 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
20 May 2026
15:30-16:30 		Alonso Beaumont
Rennes
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Alonso Beaumont, Rennes
Date, Time 20 May 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43
27 May 2026
15:30-16:30 		Francesco Lin
Columbia University
Details

Geometry Seminar

Title Title T.B.A.
Speaker, Affiliation Francesco Lin, Columbia University
Date, Time 27 May 2026, 15:30-16:30
Location HG G 43
Title T.B.A.
HG G 43

Notes: the highlighted event marks the next occurring event.

Organisers: Manfred Einsiedler, Urs Lang, Lukas Lewark, Christian Urech

Archive: SS 26 AS 25 SS 25 AS 24 SS 24 AS 23 SS 23 AS 22 SS 22 AS 21 AS 20 SS 20 AS 19 SS 19 AS 18 SS 18 AS 17 SS 17 AS 16 SS 16 AS 15 SS 15 AS 14 SS 14 AS 13 SS 13 AS 12 SS 12 AS 11 SS 11 AS 10 SS 10 AS 09 SS 09

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