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Autumn Semester 2025

Date / Time Speaker Title Location
22 September 2025
13:30-14:30 		Michael Tagaris
LAPTh, Annecy
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Talks in Mathematical Physics

Title CS-Duality, RT Construction and Observables in U(1)^n Chern-Simons Theory
Speaker, Affiliation Michael Tagaris, LAPTh, Annecy
Date, Time 22 September 2025, 13:30-14:30
Location Y27 H 25
Abstract Ιn this talk, I will address the problem of defining and computing the U(1)^n Chern–Simons (CS) partition function on closed, oriented 3-manifolds in a fully gauge-invariant framework. In contrast to usual approaches, we do not gauge fix. Instead, using the tools of Deligne–Beilinson cohomology, which naturally incorporates both differential and topological data, we work on the gauge classes of connections. By applying the reciprocity formulas of Deloup and Turaev, I will establish the so-called CS duality and demonstrate its relation to a Reshetikhin–Turaev topological invariant. Finally, I define Wilson loop observables within this framework and compute their expectation values, completing a fully consistent treatment of the theory in the closed manifold case.
CS-Duality, RT Construction and Observables in U(1)^n Chern-Simons Theoryread_more
Y27 H 25
29 September 2025
13:30-14:30 		Ezra Getzler
Northwestern University
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Talks in Mathematical Physics

Title Cyclic L-infinity algebras and shifted symplectic forms
Speaker, Affiliation Ezra Getzler, Northwestern University
Date, Time 29 September 2025, 13:30-14:30
Location Y27 H 25
Abstract A cyclic L-infinity algebra is a shifted symplectic formal derived stack. Using a new geometric approach to homological perturbation theory, we construct a shifted symplectic form on the associated derived stack. (This is a derived analogue of the correspondence between Lie algehroids and Lie groupoids.)
Cyclic L-infinity algebras and shifted symplectic forms read_more
Y27 H 25
13 October 2025
13:30-14:30 		Tsviqa Lakrec
University of Geneva
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Talks in Mathematical Physics

Title Tilings and Cluster Algebras for the Amplituhedron
Speaker, Affiliation Tsviqa Lakrec, University of Geneva
Date, Time 13 October 2025, 13:30-14:30
Location Y27 H 25
Abstract n 2005, Britto, Cachazo, Feng and Witten (BCFW) gave a recurrence relation for computing scattering amplitudes in N = 4 super Yang–Mills theory. In 2013, Golden, Goncharov, Spradlin, Vergu and Volovich discovered in the scattering amplitudes of this theory a cluster algebraic structure. The amplituhedron A(n,k,m) is a geometric object, introduced by Arkani-Hamed and Trnka in 2013, conjectured to encode scattering amplitudes in planar N = 4 super Yang–Mills. In this talk, I will discuss the amplituhedron and how both the aforementioned BCFW recursion and cluster algebra structures are manifested in it. Based on joint works with Even-Zohar, Parisi, Sherman-Bennett, Tessler and Williams.
Tilings and Cluster Algebras for the Amplituhedronread_more
Y27 H 25
* 20 October 2025
13:30-14:30 		Vladimir Dotsenko
University of Strasbourg
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Talks in Mathematical Physics

Title Higher-dimensional Givental symmetries
Speaker, Affiliation Vladimir Dotsenko, University of Strasbourg
Date, Time 20 October 2025, 13:30-14:30
Location HG G 19.1
Abstract Some 20 years ago, Chen, Gibney and Krashen introduced beautiful algebraic varieties parametrizing "pointed trees of projective spaces"; these varieties generalize the celebrated Deligne-Mumford compactifications of moduli spaces of genus zero curves with marked points. In the latter case, the homology operad encodes the tree level part of a cohomological field theory. It follows from the work of Givental and many others that the space of all such structures on a given graded vector space has a very rich symmetry group; this fact has been used in many different research areas. In this talk, I shall prove that the homology of the operad made of Chen-Gibney-Krashen spaces possesses many interesting properties, and in particular, there are higher-dimensional Givental symmetries that emerge in this story. Curiously enough, this leads to new results on classical Givental symmetries as well. This is joint work with Eduardo Hoefel, Sergey Shadrin and Grigory Solomadin.
Higher-dimensional Givental symmetriesread_more
HG G 19.1
* 20 October 2025
14:45-15:45 		Bruno Vallette
Université Sorbonne Paris Nord
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Talks in Mathematical Physics

Title Operadic Calculus for Higher Colour-Kinematics Duality
Speaker, Affiliation Bruno Vallette, Université Sorbonne Paris Nord
Date, Time 20 October 2025, 14:45-15:45
Location HG G 19.1
Abstract This talk aims at providing gauge field theory, in particular colour–kinematics duality and the double copy construction, with the required higher algebraic structures. From the algebro-homotopical perspective, a classical field theory is encoded by a cyclic homotopy Lie algebra whose Maurer–Cartan functional defines the action. For many gauge theories of interest, including Chern–Simons and Yang–Mills, this algebra splits as a tensor product of a cyclic Lie algebra, the colour Lie algebra, and a cyclic homotopy-commutative algebra, the kinematic algebra. The duality between colour and kinematics, first observed by Bern–Carrasco–Johansson in the study of Yang–Mills amplitudes, suggests that the kinematic algebra carries a Lie-type structure. For theories with at most cubic interactions, this structure is captured by coexact Batalin-Vilkovisky (BV) algebras, algebraic objects dual to the exact BV algebras arising in Poisson geometry. To incorporate higher-order interactions, following ideas of M. Reiterer, a homotopy refinement of this notion becomes necessary. The purpose of this talk is to provide a conceptual definition of homotopy coexact BV algebras, expressed in relation to homotopy commutative and BV algebras, together with a concrete operadic model. Our framework gives explicit presentations in terms of generating operations and relations and enables the systematic application of homotopical methods—including homotopy transfer, rectification, infinity-morphisms, and deformation theory—to the resulting algebras. The quartic-level structures recently identified in Yang–Mills theory fits naturally into this framework. This is a joint work with Anibal Medina-Mardones.
Operadic Calculus for Higher Colour-Kinematics Dualityread_more
HG G 19.1
3 November 2025
13:30-14:30 		Nathalie E. Rieger
Yale University
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Talks in Mathematical Physics

Title From Riemannian to Lorentzian: Embeddings of Signature-Changing Manifolds
Speaker, Affiliation Nathalie E. Rieger, Yale University
Date, Time 3 November 2025, 13:30-14:30
Location Y27 H 25
Abstract We examine a class of semi-Riemannian manifolds that undergo smooth metric signature change—from Riemannian to Lorentzian—across a hypersurface with a transverse radical. This class includes physically mo- tivated cosmological models such as the Hartle-Hawking “no-boundary” proposal, in which the universe transitions smoothly from a Euclidean to a Lorentzian phase. We show that these manifolds admit isometric embeddings into higher-dimensional pseudo-Euclidean spaces and, in particular, prove the existence of global isometric embeddings of the canonical model into both Minkowski and Misner spaces. This framework provides a mathematical setting for studying smooth signature change and its role in higher-dimensional and cosmological models.
From Riemannian to Lorentzian: Embeddings of Signature-Changing Manifoldsread_more
Y27 H 25
8 December 2025
13:30-14:30 		Eva Miranda
U. Politecnica de Catalunya
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Talks in Mathematical Physics

Title Quantizing Poisson Manifolds Through Their Symplectic Avatars
Speaker, Affiliation Eva Miranda, U. Politecnica de Catalunya
Date, Time 8 December 2025, 13:30-14:30
Location Y27 H 25
Abstract This talk presents a new approach to the quantization of Poisson manifolds with linearizable transverse Poisson structure through what I call their symplectic avatars: E-symplectic manifolds naturally associated with a given Poisson structure. These avatars provide accessible symplectic models that preserve the core features of the underlying Poisson geometry while allowing the use of powerful symplectic techniques. I will begin with the case of b-symplectic manifolds, showing how their geometric and deformation quantization can be explicitly determined and vividly illustrated in the presence of additional symmetries using the language of Delzant polytopes. This example demonstrates how singular symplectic structures offer a fertile testing ground for quantization beyond the classical smooth setting. I will conclude the talk with a desingularization theorem for linearizable transverse Poisson structures (joint work with Ryszard Nest), establishing that they can be desingularized by suitable E-symplectic avatars. I will discuss how this desingularization principle opens new avenues for both geometric and deformation quantization, effectively bridging Poisson and symplectic worlds.
Quantizing Poisson Manifolds Through Their Symplectic Avatarsread_more
Y27 H 25
15 December 2025
13:30-14:30 		Ödül Tetik
University of Vienna
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Talks in Mathematical Physics

Title A generalised Poisson additivity
Speaker, Affiliation Ödül Tetik, University of Vienna
Date, Time 15 December 2025, 13:30-14:30
Location Y27 H 25
Abstract The Poisson additivity theorem of Rozenblyum–Safronov gives an equivalence between the category of n-disk algebras valued in 1-shifted Poisson algebras and the category of (1-n)-shifted Poisson algebras. Seeing this as a topological statement on a coordinate patch, I will discuss a generalisation of this theorem to a non-topological statement on arbitrary (but non-stratified) spacetimes, building on an approach due to Tamarkin. The key novel notion is that of a factorisation Lie algebra. This is joint work in preparation with Giovanni Canepa and Nils Carqueville.
A generalised Poisson additivityread_more
Y27 H 25

Notes: events marked with an asterisk (*) indicate that the time and/or location are different from the usual time and/or location.

Archive: AS 25 SS 25 AS 24 SS 24 AS 23 SS 23 AS 22 SS 22 AS 21 SS 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

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