Date | Speaker | Title | Abstract | Note |
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26.1.17 | Hans Franzen (Bochum University) | Donaldson-Thomas invariants of quivers via Chow groups of quiver moduli | We use a presentation of Chow rings of (semi-)stable quiver moduli to show that the primitive part of the Cohomological Hall algebra of a symmetric quiver is given by Chow groups of moduli of simple representations. This implies that the DT invariants are determined by these Chow groups. | Seminar, 3pm, OSR |

26.1.17 | Hans Franzen (Bochum University) | Geometric properties of quiver Grassmannians | Quiver Grassmannians are geometric objects which parametrize subrepresentations of quiver representations. They can ban be regarded as analogs of (the usual) Grassmannians. Caldero and Chapoton have shown that the cohomology of quiver Grassmannians plays an important role in the theory of cluster algebras. After giving a basic introduction to representations of quivers and quiver Grassmannians, we exhibit classes of representations for which the quiver Grassmannian has a very simple geometric structure. | Colloquium, 5pm, Synge |

2.2.17 | Norbert Hoffmann (Mary Immaculate College, Limerick) | Del Pezzo surfaces and universal torsors | A homogenuous polynomial equation of degree three in four variables defines a cubic surface S in complex projective threespace. Manin's Conjecture relates the geometry of this complex surface S to integer solutions of the equation. A main tool to study such integer solutions are the universal torsors over S introduced by Colliot-Thelene and Sansuc. All this generalizes from cubic surfaces to more general del Pezzo surfaces. After explaining this, I will speak about recent joint work with Ulrich Derenthal on universal torsors over degenerating del Pezzo surfaces. | Colloquium, 5pm, Synge |

9.2.17 | G. Gabadadze Yu. Tschinkel A. Okounkov |
HMI mini-conference | ||

10.2.17 | M. Kontsevich N. Nekrasov |
HMI mini-conference | ||

16.2.17 | Antonio Giambruno (Palermo University) | Polynomial identities and their growth | A polynomial identity satisfied by an algebra A is a polynomial in non commuting indeterminates vanishing identically when evaluated in A. These polynomials form a T-ideal of the free algebra, i.e., an ideal invariant under the endomorphisms of the free algebra. In general one can attach to such a T-ideal a numerical sequence, called the sequence of codimensions of A. In characterstic zero this sequence gives a quantitative measure of the polynomial identities satisfied by the algebra A. The aim of this talk is to present some of the results obtained in recent years on the asymptotic computation of such sequence. As a by-product I shall describe a method based on the representation theory of the symmetric group leading to some classification results. | Colloquium, 5pm, Synge |

23.2.17 | Sung Yeon Kim (CMC, KIAS) | CR maps between boundaries of flag domains | Colloquium, 5pm, Synge | |

16.3.17 | Leandro Vendramin (University of Buenos Aires) | Nichols algebras and applications | Nichols algebras appear in several branches of mathematics going from Hopf algebras and quantum groups, to Schubert calculus and conformal field theories. In this talk we review the main problems related to Nichols algebras and we discuss some classification theorems and some applications. | Seminar, 2pm, OSR |

16.3.17 | Brent Pym (University of Edinburgh) | Divergent series and the Stokes groupoids | Near a point where an ordinary differential equation has a pole of order two or more, its solutions may have very complicated behaviour, including essential singularities and divergent power series expansions. Nevertheless, using natural objects of differential geometry known as Lie groupoids, one can construct a canonical domain on which the solutions are globally defined and holomorphic. I will describe this construction and explain how it gives a new geometric interpretation of the classical techniques for "resumming" divergent series. This talk is based on joint work with Marco Gualtieri and Songhao Li. | Colloquium, 5pm, Synge |

30.3.17 | Franc Forstnerič (University of Ljubljana) | Complete bounded submanifolds in different geometries | In this lecture I will survey recent results on the construction of bounded metrically complete submanifolds in several different geometries: holomorphic submanifolds of complex Euclidean spaces (the problem of Paul Yang), null holomorphic curves and conformal minimal surfaces in Euclidean spaces (the Calabi-Yau problem), and complete Legendrian curves in contact complex manifolds. | Colloquium, 5pm, Synge |

7.4.17 | Kobi Kremnitzer (Oxford University) | TBA |

Date | Speaker | Title | Abstract | Note |
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29.9.16 | Emilio Franco (Unicamp, Brazil) | Brane involutions and irreducible holomorphic symplectic manifolds | We study natural brane-involutions on moduli space of sheaves over symplectic surfaces and their behaviour under Fourier-Mukai transform and lattice Mirror symmetry. This is joint work with M. Jardim (Campinas State University) and G. Menet (Campinas State University). | |

6.10.16 | Victoria Lebed (TCD) | Unexpected facets of the Yang-Baxter equation | In this talk I propose to look at the good old Yang-Baxter equation from an unexpected viewpoint. We shall see that this equation generalizes basic algebraic laws: associativity, the Jacobi identity, self-distributivity, the axioms of a lattice. In spite of this generality, one can say non-trivial things valid for all solutions to the YBE - namely, concerning their representation and (co)homology theories. Moreover, any solution comes with a quadratic universal enveloping algebra, which for certain solution classes enjoys particularly nice algebraic properties. As an application, we shall outline how to construct resolutions of some algebras by interpreting them as the universal enveloping algebras of easily manipulable solutions to the YBE. Knot-theoretic applications will also be sketched. | Mathematics Colloquium Synge 5pm |

13.10.16 | Jonas Kaszian (University of Cologne) | Indefinite Theta Functions arising in Gromov-Witten Theory | In this talk, we consider a function occuring naturally in the open Gromov-Witten potential of an elliptic orbifold. To help illuminate its mysterious nature, we connect it with higher-depth mock modular forms by studying related indefinite theta functions of signature (1,3). The study of these functions was recently opened up by work of Alexandrov, Banerjee, Manschot, and Pioline discussing the case of signature (n,2). | |

20.10.16 | Raf Bocklandt (University of Amsterdam) | Moduli of Matrix factorizations | We discuss how to construct moduli spaces of matrix factorizations using concepts from mirror symmetry and illustrate these ideas with examples coming from dimer models. | |

From the Freezer to the Tropics | Following Goncharov and Kenyon one can define a dynamical system from a consistent dimer model. On the other hand one can also use this dimer model to resolve a singularity. We will explain how these two become related if we go to the absolute zero temperature in the dynanical system and to the tropical limit of the resolution. | Mathematics Colloquium Synge 5pm |
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27.10.16 | Emmanuel Letellier (Paris Diderot-Paris 7 University) |
Higgs bundles and indecomposable parabolic vector bundles over the projective line | In this talk we will count the number of isomorphism classes of geometrically indecomposable parabolic bundles over the projective line over a finite field. We will explain the relation between this counting and the moduli space of Higgs bundles with prescribed residues over the complex projective line. | |

Character varieties and representation theory | The aim of this talk is to explain the relation between two problems in mathematics: the first one is about the representation theory of finite Lie groups and the second one is about the geometry of the so-called character varieties, namely the moduli space of representations of the fundamental groups of punctured compact Riemann surfaces into complex Lie groups. | Mathematics Colloquium Synge 5pm |
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17.11.16 | Herve Gaussier (Grenoble) | How can metrics explain some geometric properties of complex manifolds? | The Poincaré distance is an example of a hyperbolic distance on the unit disk in C. It admits different generalizations in the context of complex geometry, such as the Bergman metric, example of a Kähler-Einstein metric, or the Kobayashi metric, example of a Finsler metric, defined on complex manifolds. We will explain how the properties of such metrics restrict the geometry of the manifold. | Mathematics Colloquium Synge 5pm |

24.11.16 | Tyler L. Kelly (University of Cambridge) | Unifying Mirror Constructions | Mirror symmetry uses dualities in string theory to predict that, given a symplectic variety, there should exist an algebraic variety known as the mirror such that various geometric and physical data are exchanged. Over the past 25 years, there have been many recipes that have been proposed to construct the mirror for certain symplectic varieties. However, in certain cases, for the same symplectic variety, different recipes can give different algebraic varieties as the mirror. In this talk, we will talk about how one can fix this discrepancy in the context of Kontsevich's Homological Mirror Symmetry. | Mathematics Colloquium Synge 5pm |

1.12.16 | Arnaud Mortier (DCU) | Finite-type cohomology of the space of long knots | The aim of this talk is to give an overview of Vassiliev's cohomology of the space of knots. Topics discussed will include the origins in singularity theory, several algebraic reformulations, the Kontsevich integral (a universal Vassiliev knot invariant), a systematic way to construct cocycles, and some examples. | |

Knots, virtual knots, and finite-type invariants | In the classical sense, a knot is an embedding of a circle in R^3. This notion has known a multitude of variations, with as many purposes: trading the circle for another 1-manifold, increasing dimensions... Virtual knot theory is such a variation. It came up during the 90's after a period of enthusiasm towards a new kind of knot invariants, today widely understood except for the fact that it is still open whether they classify all knots: Vassiliev's 'finite-type' invariants. I will discuss the main ideas behind these notions. | Mathematics Colloquium New sem. room 4:30pm |
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9.12.16 | Nikos Diamantis (University of Nottingham) |
Values of L-functions and shifted convolutions | A characterisation of the field containing the values of L-functions is proposed. This is described in terms of shifted convolution series of divisor sums and to establish it we use a double Eisenstein series we previously studied with C. O'Sullivan and a kernel function used by F. Brown in his study of multiple modular values. | Mathematics Colloquium Synge 4pm |

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