\;
\nIm Rahmen des Oberseminars Analysis/Numerik spricht
\n\;
\n\;
\nAb stract "This talk is about self-adjointnes s and regularity of the Dirac operator with boundary values on domains wit h singularities. We first review known results on twodimensional corner do mains and on convex domains with MIT-boundary conditions. We extend this t heory to higher-dimensional conical domains with generic local boundary co nditions
\n\;
\nThe key idea is to locally transform the Di rac operator under general boundary conditions on a conical domain near th e singularities into a perturbed Dirac operator under MIT boundary conditi ons on the model cones. This process introduces a perturbation that can be handled via the Kato-Rellich Theorem. In the model case\, the theory reli es heavily on the separation ansatz and a spectral gap on the link of the cone\, which ultimately ensures self-adjointness and regularity."\n
\;
\n
\;
Im Rahmen des Oberseminars Analysis/Numerik s pricht
\nüber
\nAbstract: The uncertainty principle in harmonic
analysis states that a non-zero function and
its Fourier transform ca
nnot be simultaneously too sharply localized. There are numerous
prec
ise mathematical formulations of this meta-theorem.
The talk is based on collaborative work with Lenny N
eyt (University of Vienna).
\;
Der Vortrag findet statt am Donnerstag\, den 18.06.2026
u
m 14.30 – 15.30 Uhr im Raum W01 1-117
\;
\n\;
LOCATION: END:VEVENT BEGIN:VEVENT UID:calendarize-affine-chabauty DTSTAMP:20260609T134005Z DTSTART:20260616T170000Z SUMMARY:Affine Chabauty DESCRIPTION:Vortragsankündigung\nIm Rahmen des Oberseminars Algebra spric ht\nHerrn Martin Lüdtke\n(Universität Oldenburg)\nTitle: Affine Chabaut y\n \nAbstract: Given a hyperbolic curve Y defined over the integers and a finite set of primes S\, the theorems of Siegel\, Mahler\, and Faltings guarantee that the set of S-integral points Y(Z_S) is finite.\nDetermining this set in practice is a difficult problem for which no general method i s known. In the case of projective curves\, Chabauty's method can often be used to produce a finite subset of the p-adic points containing the ratio nal points. I present a Chabauty method for affine curves based on embed ding the curve in its generalised Jacobian and constraining the image of t he S-integral points via arithmetic intersection theory. This is joint wo rk with M. Leonhardt.\n \nDer Vortrag findet statt am\n \nDienstag\, den 16.06.2026um 17.00 Uhr im Raum W01 0-006\n \n \nInteressierte sind herz lich eingeladen. X-ALT-DESC;FMTTYPE=text/html:Im Rahmen des Oberseminars Algeb ra spricht
\n(Universität Oldenburg)
\n&nbs p\;
\nAbstr act: Given a hyperbolic curve Y defined over the integers and a f inite set of primes S\, the theorems of Siegel\, Mahler\, and Faltings gua rantee that the set of S-integral points Y(Z_S) is finite.
\nDetermining this set in p ractice is a difficult problem for which no general method is known. In th e case of projective curves\, Chabauty's method can often be used to produ ce a finite subset of the p-adic points containing the rational points.&nb sp\; I present a Chabauty method for affine curves based on embedding the curve in its generalised Jacobian and constraining the image of the S-inte gral points via arithmetic intersection theory. \;This is joint work with M. Leonhardt.
\n\;
\nDer Vortrag findet statt am
\n&nb sp\;
\nDienstag\, den 16.06.2026
um
17.00 Uhr im Raum W01 0-006
\;< /p>\n
\;
\nInteressierte sind herzlich e ingeladen.
LOCATION: END:VEVENT BEGIN:VEVENT UID:calendarize-generic-homogeneous-polynomial-mappings-of-c4-to-c4-and-th eir-singularities DTSTAMP:20260609T135138Z DTSTART:20260616T160000Z SUMMARY:GENERIC HOMOGENEOUS POLYNOMIAL MAPPINGS OF C4 TO C4 AND THEIR SING ULARITIES DESCRIPTION:Vortragsankündigung\nIm Rahmen des Oberseminars Algebra spric ht\n \nHerr Dr. Joao Pissolato\n(Sao Carlos)\n \n \nDer Vortrag findet statt am\nDienstag\, den 16.06.2026um 16.00 Uhr im Raum W01 0-006\nInteres sierte sind herzlich eingeladen.\n\n X-ALT-DESC;FMTTYPE=text/html:Im Rahmen des O berseminars Algebra spricht
\n\;
\n& nbsp\;
\n
\;
Der Vortrag findet statt am
\nDienstag\, den 16.06.2
026
um 16.00 Uhr im Raum W01 0-006
Interessierte sind herzlich eingeladen.
\n\n LOCATION: END:VEVENT BEGIN:VEVENT UID:calendarize-finsler-spacetime-geometry-and-the-gravitational-field-of- kinetic-gases DTSTAMP:20260528T110930Z DTSTART:20260611T143000Z DTEND:20260611T153000Z SUMMARY:Finsler spacetime geometry and the gravitational field of kinetic gases DESCRIPTION:Vortragsankündigung\n \nIm Rahmen des Oberseminars Analysis/ Numerik spricht\nHerr Dr. Christian Pfeifer\n(ZARM\, Universität Bremen)\ nüber\nFinsler spacetime geometry and the gravitational field of kinetic gases\n \nAbstract: Pseudo-Finsler manifolds generalize pseudo-Riemannian manifolds in a straightforward manner. The geometry of a Finslerian manif old is derived from a general pseudo-norm\, analogously to how the geometr y of pseudo-Riemannian manifolds is derived from a metric tensor. In physi cs\, pseudo-Finsler geometry is a viable and highly interesting candidate for an extended geometry of spacetime that can provide an improved descrip tion of gravitational interaction beyond general relativity\, potentially offering a geometric understanding of dark matter and dark energy. From a mathematical perspective the study of pseudo-Finsler geometry offers\, amo ng others\, interesting applications to optimisation problems\, inequaliti es or the question of metrizabillity of affine connections.\nIn this talk\ , I will discuss the Finsler gravity framework as extension of general rel ativity\, and demonstrate that in homogeneous and isotropic symmetry\, the Finsler gravity equation possesses solutions that describe an accelerated expanding universe\, without the need of a cosmological constant or any o ther additional fields. I will introduce the concept of Finsler spacetimes and their classification according to their deviation from pseudoRiemanni an geometry. Afterwards I will focus on the Finsler gravity equation\, the coupling between Finsler geometry and the kinetic gas\, and how the Finsl er gravity equation takes a Friedmann equation like form in homogeneous an d isotropic symmetry. Finally we will see that this Finsler Friedmann equa tion allows for vacuum solutions that describe an exponentially expanding universe\, which is a first direct indication that Finsler spacetimes are capable to address the nature of dark energy. \n \nDer Vortrag findet st att am\nDonnerstag\, den 11.06.2026 um 14.30 – 15.30 Uhr im Raum W01 1-1 17\nInteressierte sind herzlich eingeladen. X-ALT-DESC;FMTTYPE=text/html:\;
\nIm Rahmen des Oberseminars Analysis/Numerik spricht
\n\;\n
Abstract: Pseudo-Finsler manifolds generalize pseudo-Riemannian manifolds in a straightforward manner. The geometry of a Finslerian manifo ld is derived from a general pseudo-norm\, analogously to how the geometry of pseudo-Riemannian manifolds is derived from a metric tensor. In physic s\, pseudo-Finsler geometry is a viable and highly interesting candidate f or an extended geometry of spacetime that can provide an improved descript ion of gravitational interaction beyond general relativity\, potentially o ffering a geometric understanding of dark matter and dark energy. From a m athematical perspective the study of pseudo-Finsler geometry offers\, amon g others\, interesting applications to optimisation problems\, inequalitie s or the question of metrizabillity of affine connections.
\nIn this talk\, I will discuss the Finsler gravity framework as extension of general relativity\, and de monstrate that in homogeneous and isotropic symmetry\, the Finsler gravity equation possesses solutions that describe an accelerated expanding unive rse\, without the need of a cosmological constant or any other additional fields. I will introduce the concept of Finsler spacetimes and their class ification according to their deviation from pseudoRiemannian geometry. Aft erwards I will focus on the Finsler gravity equation\, the coupling betwee n Finsler geometry and the kinetic gas\, and how the Finsler gravity equat ion takes a Friedmann equation like form in homogeneous and isotropic symm etry. Finally we will see that this Finsler Friedmann equation allows for vacuum solutions that describe an exponentially expanding universe\, which is a first direct indication that Finsler spacetimes are capable to addre ss the nature of dark energy. \;
\n&n bsp\;
\nDer Vortrag fin det statt am
\n< strong>Donnerstag\, den 11.06.2026 um 14.30 – 15.30 Uhr im Raum W01 1-11 7
\n\;
\nI m Rahmen des Oberseminars Analysis/Numerik spricht
\nüber
\n\;
\nAbstract: In this talk\, we study the spectral properties of manifolds with si ngularities obtained as quotients of the hyperbolic upper half-plane by He cke triangle groups. These manifolds are geometrically complicated (they m ay have infinite volume and up to two types of singularities)\, but simple from the perspective of the fundamental group (having only two generators and one relation). To study their spectral properties\, we consider the a ssociated Selberg zeta functions\, whose zeros correspond to resonances of the surfaces. We show that the Selberg zeta function can be approximated by determinants of finite matrices throughout its domain of holomorphy. Fo r certain manifolds\, such approximations allow to compute the base eigenv alues of the Laplace operators to 50-digit precision within 5 seconds usin g interval arithmetic. Additionally\, we investigate the location of non-r eal resonances and observe that\, for large funnel widths\, they appear to organize into resonance chains almost satisfying functional equations inv olving the Riemann zeta function.
\n\;
\nInteressierte sind he
rzlich eingeladen. \;
\;
übe
r
Abstract: We investigate the spectrum of the first-or
der operator that governs the propagation
of electromagnetic waves in
the case of a closed locally perturbed waveguide filled with a
hyper
bolic medium. The perturbation is localized on the boundary and we impose<
br />homogeneous Dirichlet boundary conditions.
From a physics perspe
ctive\, this type of medium falls within the class of hyperbolic
elec
tromagnetic metamaterials. They are artificial media which exhibit a lot o
f interesting and
promising physics phenomena such as negative refrac
tion\, rainbow-trapping and enhanced
spontaneous emission.
In pr
actice\, the simplest mathematical model stems from electromagnetic wave p
ropagation in
a strongly magnetized cold plasma. It is described by 2
D Maxwell equations which\, in their
time-harmonic form\, may be redu
ced to the Klein-Gordon equation for a certain range of
frequencies\,
namely the hyperbolic frequencies. Hence\, the nature of the problem is p
urely
hyperbolic.
Firstly\, we prove a limiting absorption princ
iple (LAP) for the hyperbolic frequencies satisfying
a geometric cond
ition on the perturbation. The latter is related to the interplay between
the
velocities of the boundary and of the propagating waves\, which\,
in our case\, depends on the
frequency. This range of frequency is c
alled the subsonic regime. The key idea of our work is
the use of the
well-posedness and energy estimates of the Klein-Gordon equation in bound
ed
time-dependent domains.
The second part of the talk will be d
evoted to the 'supersonic' regime: the frequencies for which
the boun
dary moves faster than the waves. In particular\, the Klein-Gordon equatio
n in arbitrary
time-dependent domains is no longer well-posed for hom
ogeneous Dirichlet boundary
conditions. Nevertheless\, we are still a
ble to prove a LAP by using the weak observability
results of waves a
nd exchanging the role of the time and space variables.
\;
Interessierte sind herzlich eingeladen.
\;
\nIm Rahmen des Oberseminars Analysis/Numerik spricht\n
\;
\nüber
\n\;
\n\;
\nAbstract: \;One of the most fundamental principles used in theoretical physics is the sta tionary action principle. It states that the classical solutions of a phys ical system are the stationary solutions of an action functional\, defined on its phase space. This leads to the Euler-Lagrange equations by applyin g variational calculus\, in a straightforward calculation. A more difficul t question is the so-called inverse problem of variational calculus: given a set of differential equations\, 1. do these equations arise from variat ion of an action\, 2. how to find the action? Both questions can be answer ed by the method of variational completion\, and calculating the so-called Vainberg-Tonti Lagrangian. However\, this classical method is dependent o n the choice of coordinates\, and requires certain conditions on the domai n of definition of the system. In my talk\, I present the proper geometric framework for the Lagrange formalism and the inverse problem in terms of jet bundles\, at a beginner level. Then I show how the classical Vainberg- Tonti procedure can be generalized in a coordinate-independent fashion.&nb sp\;
\n\;
\nDer Vortrag findet statt am
\n\;
\nDonnerstag\, den 30.04.2026
um 14.30
– 15.30 Uhr im Raum W01 1-117
&nbs p\;
\n\;
\nIntere ssierte sind herzlich eingeladen.
\n\;
LOCATION: END:VEVENT BEGIN:VEVENT UID:calendarize-stochastic-completeness-and-the-calabi-yau-conjectures DTSTAMP:20260422T091345Z DTSTART:20260423T151500Z DTEND:20260423T160000Z SUMMARY:Stochastic completeness and the Calabi-Yau conjectures DESCRIPTION:Vortragsankündigung\nIm Rahmen des Oberseminars Analysis/Nume rik sprichtHerr Dr. Giuseppe Gentile\nüber\nStochastic completeness and t he Calabi-Yau conjectures\nAbstract: In this talk I will present recent de velopments on the geometric properties of minimalsubmanifolds and harmonic maps\, motivated by the classical Calabi-Yau conjectures. Theseconjecture s predict that minimal hypersurfaces in Euclidean space\, as well as certa in of theirprojections\, must be unbounded. While striking counterexamples show that the conjectures failin general for immersed surfaces\, they rem ain true under additional geometric assumptions. Iwill explain how stochas tic completeness\, viewed as a weak maximum principle for noncompact manif olds\, together with a flexible notion of convexity (pullvexity)\, can be used torecover such unboundedness results. This is joint work with Renan A ssimos and BalázsBékési.\nDer Vortrag findet statt amDonnerstag\, den 2 3.04.2026um 15.15 – 16.00 Uhr im Raum W01 1-117\nInteressierte sind herz lich eingeladen. X-ALT-DESC;FMTTYPE=text/html:über
\n
Abstract: In this talk I will present recent developments on the ge
ometric properties of minimal
submanifolds and harmonic maps\, motiva
ted by the classical Calabi-Yau conjectures. These
conjectures predic
t that minimal hypersurfaces in Euclidean space\, as well as certain of th
eir
projections\, must be unbounded. While striking counterexamples s
how that the conjectures fail
in general for immersed surfaces\, they
remain true under additional geometric assumptions. I
will explain h
ow stochastic completeness\, viewed as a weak maximum principle for noncom
pact manifolds\, together with a flexible notion of convexity (pullvexity)
\, can be used to
recover such unboundedness results. This is joint w
ork with Renan Assimos and Balázs
Békési.
Der Vortrag findet statt am
Donnerstag\, den 23.04.
2026
um 15.15 – 16.00 Uhr im Raum W01 1-117
Interessierte sind herzlich eingeladen.
Vortragsankündigung
\n\;
\nIm Rahmen des Oberseminars A nalysis/Numerik spricht
\nHerr Dr. Alexey Ryabov
\n(ICBM\, Universität Oldenburg)
\nüber< /p>\n
\;
\nAbstract: In this presentation\, I will discu ss a critical problem in ecological modeling\, which I
\nrefer to here as the "modelers' t ragedy". This challenge arises because to model ecological
\nsystems we have to rely on in complete functional relationships\, usually obtained in laboratory< /p>\n
conditions. These rel ationships often cover only a few factors\, failing to represent the natur e
\ncomplexity a nd omitting factors for which there is insufficient data. It's like puttin g together a
\np uzzle with missing pieces - a real tragedy. Even when we carefully fit par ameters enabling
\nmodels to predict dynamics over a given period\, doubts remain about th e accuracy of the model
\nin reflecting true internal processes and its future predictive power.
\nTo solv e this problem\, we propose a new approach: "nonparametric population dyna mic
\nmodeling". This method abandons predefined functional relationships by extracting th is
\ninformation directly from field data. We combine dynamic modeling with a machine lear ning
\ntechnique known as parameter regularization\, aiming to identify the simplest model s that best
\nge neralize the data.
\n\;
\nOur process begins with fitting a baseline model to a time series of species abundance\,
\nassuming e.g. constant birth and death rates. We then determine the minimum parameter
\ndeviations needed at each time poi nt of observation (e.g.\, annually) to accurately reflect
\npopulation dynamics. By analyz ing how these parameter deviations relate to environmental
\nfactors\, we determine enviro nmental effects on population growth and loss rates.
\nWe demonstrate this method using th e example of Antarctic krill\, a key species in the
\nSouthern Ocean's fishery and food we b. Our approach determines how variables such as
\ntemperature\, food availability\, and i ce cover affect krill population losses throughout the year
\nand at different life stages . Ultimately\, we show how these findings can be incorporated into a
\nstatistical dynamic model that describes the population dynamics of Antarctic krill.\n
1. A. Ryabov\, U. Berg er\, B. Blasius\, B. Meyer\, Driving forces of Antarctic krill abundance.< /span>
\nScience Advanc es 9\, eadh4584 (2023). https://www.science.org/doi/10.1126/sciadv.adh4584
\n\;
\nFakultät V
&nbs p\;
\nMathematik und Na turwissenschaften
\n\;
\nDer Vortrag findet statt a m
\n\;
\nInteressierte sind herzlich eingeladen. \;
\;
\;
\nIm Rahmen des Oberseminars Analysis/Numerik spricht
\nFrau Prof. Dr. Anna Siffert
\n(Universität Münster )
\nüber
\nAbstract:
In this talk we present\, \;a construction method of r-harmonic maps
to spheres.
We in particular construct an explicit family of stable p
roper weak biharmonic maps from the
unit ball.
This is joint wor
k with Volker Branding.
Der Vortrag fin det statt am
\nDonnerstag\, den 16.04.20 26 um 14.30 – 15.30 Uhr im Raum W01 1-117
\nInteressierte sind herzlich eingeladen.
\n\;
LOCATION: END:VEVENT BEGIN:VEVENT UID:calendarize-homological-indices-and-local-riemann-roch-type-theorems DTSTAMP:20260408T144005Z DTSTART:20260414T141500Z DTEND:20260414T154500Z SUMMARY:Homological indices and local Riemann-Roch type theorems DESCRIPTION:Vortragsankündigung\nIm Rahmen des Oberseminars Algebra/Geome trie spricht \nHerr Dr. Matthias Zach (Uni Kaiserslautern)\nüber\nHomolo gical indices and local Riemann-Roch type theorems\nA homological index is the Euler characteristic of a complex of coherent sheaves with finite sup port. Local Riemann-Roch type theorems relate them to intersection numbers and Chern classes\, i.e. objects of topological nature. In complex analyt ic singularity theory we can thus use such theorems to compute topological invariants by algebraic methods. I will report on the toolbox in the comp uter algebra system OSCAR which we have made available to this end\, from Gröbner bases building on Singular's core functionality up to the W-funct or for the computation of direct images for the ``derived homological inde x''.\n \nDienstag 14.04.2026 um 14:15 UhrRaum W01 0-015 \n \nInteressie rte sind herzlich eingeladen X-ALT-DESC;FMTTYPE=text/html:ü ber
\nA homologica l index is the Euler characteristic of a complex of coherent sheaves with finite support. Local Riemann-Roch type theorems relate them to intersecti on numbers and Chern classes\, i.e. objects of topological nature. In comp lex analytic singularity theory we can thus use such theorems to compute t opological invariants by algebraic methods. I will report on the toolbox i n the computer algebra system OSCAR which we have made available to this e nd\, from Gröbner bases building on Singular's core functionality up to t he W-functor for the computation of direct images for the ``derived homological index''.
\n\;
\n< p class="text-center">Dienstag 14.04.2026 um 14:15 Uhr\;
\n