Monday,
20180423
16:1517:45

Raum 404, ErnstZermeloStr. 1
Fornasin, Hou, Kertels, Lye:
Gong Show: What I found on the arXiv 
Monday,
20180430
16:1517:45

Raum 404, ErnstZermeloStr. 1
Fornasin, Hou, Kertels, Lye:
Gong Show: What I found on the arXiv 
Monday,
20180507
16:15

Raum 404, ErnstZermeloStr. 1
Lorant Szegedy (Hamburg):
Topological field theory on rspin surfaces and the Arf invariant
We present a statesum construction of TFTs on rspin surfaces which uses a combinatorial model of rspin structures. We give an example of such a TFT which computes the Arf invariant for r even. We use the combinatorial model and this TFT to calculate diffeomorphism classes of rspin surfaces with parametrized boundary. 
Monday,
20180507
17:1518:15

Raum 404, ErnstZermeloStr. 1
Prof. Charles Doran (University of Alberta, ICERM@Brown University):
Hodge Numbers from Differential Equations
A natural way of constructing CalabiYau manifolds is to build them as fibrations whose fibers are CalabiYau manifolds of lower dimension. For example, elliptic curves can be thought of as fibrations over the projective line by pairs of points, and K3 surfaces fibered over the projective line by elliptic curves form a large class of interesting K3 surfaces. In higher dimensions, the question of computing the Hodge numbers of such CalabiYau manifolds becomes a nontrivial one. I’ll talk about a method of computing Hodge numbers starting from the PicardFuchs differential equation of a family of CalabiYau manifolds. Applying this to families of latticepolarized K3 surfaces provides a key ingredient in the classification of fibered CalabiYau threefolds. 
Monday,
20180514
16:1517:45

Raum 404, ErnstZermeloStr. 1
Fornasin, Hou, Kertels, Lye:
Gong Show: What I found on the arXiv 
Monday,
20180528
16:1517:15

Raum 404, ErnstZermeloStr. 1
Jørgen Olsen Lye:
On stable, closed geodesics on a K3
I will report on the search for stable, closed geodesics on a K3 surface. In particular, I will sketch the BourguignonYau proof of why the Riemann tensor vanishes along such geodesics, and I will explain how to find totally geodesic tori in highly symmetric Kummer K3s. 
Monday,
20180604
16:15

Raum 404, ErnstZermeloStr. 1
Mark Gross FRS (Cambridge):
A general mirror symmetry construction
I will talk about joint work with Bernd Siebert, which aims to give a general construction of mirrors to either log CalabiYau manifolds or maximal degenerations of CalabiYau manifolds. The construction goes by way of building the coordinate ring of the mirror as an abstract ring whose multiplication law is governed by counting curves on the original (log) CalabiYau. 
Monday,
20180611
16:15

Raum 404, ErnstZermeloStr. 1
Wilderich Tuschmann (Karlsruhe):
Moduli Spaces of Nonnegatively Curved Riemannian Metrics
I will report on general results and questions about spaces and moduli spaces of Riemannian metrics
with nonnegative Ricci or nonnegative sectional curvature on closed and open manifolds,
and present recent joint work with Michael Wiemeler. In particular,
we construct the first classes of manifolds for which these spaces
have nontrivial rational homotopy, homology and cohomology groups. 
Monday,
20180618
16:15

Raum 404, ErnstZermeloStr. 1
Oliver Lindblad Petersen (Hamburg):
Wave equations with initial data on compact Cauchy horizons
Wave equations are usually studied in globally hyperbolic regions of
spacetimes. However, to approach the famous strong cosmic censorship
conjecture, this is not sufficient. One needs to understand the behavior
of waves close to the boundary of the globally hyperbolic region, the
Cauchy horizon. The purpose of this talk is to discuss the
characteristic Cauchy problem with initial data on a compact Cauchy
horizon. We prove an energy estimate close to compact nondegenerate
Cauchy horizons which implies existence and uniqueness results for wave
equations. In particular, we overcome the essential remaining difficulty
in proving the MoncriefIsenberg conjecture in the nondegenerate case.
This can be seen as a special case of the strong cosmic censorship
conjecture. 
Monday,
20180625
16:15

Raum 404, ErnstZermeloStr. 1
Michele Schiavina (UC Berkeley and MPIM Bonn):
Equivalence of field theories in the BVBFV formalism. Insights from General Relativity
The standard notion of equivalence of field theories roughly requires the EulerLagrange loci of the two associated variational problems to be diffeomorphic, possibly modulo the action of the respective symmetry distributions, in some appropriate framework.
This can be made stated more precisely in the BatalinFradkinVilkovisky setting, where some cohomological presentation of said locus is constructed.
I will discuss a series of examples, all related to General Relativity in different spacetime dimensions, that suggest that higher codimension data should play a role in defining (and refining) equivalence between classical theories, and raise the question of whether (and how) this picture carries over to quantisation. 
Monday,
20180702
16:15

Raum 404, ErnstZermeloStr. 1
D. Hein:
Introduction to contact dynamics
This talk will be an introduction to contact geometry and dynamics.
In particular, I will explain the relation between Hamiltonian systems and contact dynamics.
The main examples are level sets of Hamiltonians from classical mechanics and contact manifolds, ob which the Reeb flow induces an S^1action with reasonably nice quotients. 
Monday,
20180709
16:15

Raum 404, ErnstZermeloStr. 1
Ksenia Fedosova:
Vectorvalued automorphic functions and their Fourier series 
Monday,
20180716
16:15

Raum 404, ErnstZermeloStr. 1
Julian Strohm:
The Weyl Denominator Identity in light of the structure of root systems
The Weyl Denominator Identity arises usually as a special case of the Weyl Character Formula of a complex semisimple Lie algebra. Even though it prominently features the roots of the Lie algebra, the original proof provides limited insight into the structure of the root system.
I will therefore present a direct proof of the Denominator Identity. This alternative approach explicitly uses connections between the roots and the Weyl Group and might provide a different perspective on the Denominator Identity as well as the structure of the root system. 