Exceptional collections and degenerations of varieties
Date:  September 1  5, 2008  
Place:  IPMU, Seminar room at Prefab.B  
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Abstract: 
Klaus Altmann, Free Universitaet, Berlin, Germany Title: Deformation of flag quivers (with Duco van Straten) Connected quivers without oriented cycles give rise to Fano varieties being the moduli space of stable quiver representations. Via Batyrev's construction, they host CalabiYau spaces with the same type of singularities. We show that for a certain type of quivers, the Fano (and hence the CY varieties) are smoothable in codimension three. Since the obstruction spaces T2 are, in general, nontrivial, this requires a careful analysis of the multidegrees carrying nonzero T2 parts. The name flag quiver arises from the fact that the toric degeneration of flag varieties is a special case of this situation. Sergei Galkin, free artist, Moscow, Russia Title: Degenerations of Fano threefolds (towards exceptional collections) We will discuss small degenerations of smooth Fano threefolds (like V5) to toric nodal Fano threefolds and some applications of these for computing GromovWitten invariants and constructing exceptional collections on the primary smooth threefolds. Kentaro Hori 1, IPMU, Kashiwa, Japan Title: Mirror Symmetry in 2+1 and 1+1 dimensions I discuss how mirror symmetry in 1+1 dimensions and 2+1 dimensions are related. I report on a progress, as an application, to find the mirrors of Grassmannians and other flag varieties that fix a problem in the mirror conjecture by Eguchi, Xiong and myself. The latter conjecture was also considered by Batyrev, CiocanFontanine, Kim and van Straten using toric degenerations. This is based on a work with Aganagic, Karch and Tong. Kentaro Hori 2, IPMU, Kashiwa, Japan Title: Witten index of 2d supersymmetric QCD We compute the Witten index of 2d (2,2) supersymmetric QCD with twisted masses. This is based on a work with David Tong. Possible relation to exceptional collections in Grassmannians may be discussed, possibly. Hiroshige Kajiura, Chiba University, Japan Title: Strongly exceptional collections associated to regular systems of weights with ε = 1. I plan to talk about strongly exceptional collections of the triangulated categories of graded matrix factorizations associated to regular system of weights with ε = 1, where the strongly exceptional collections give examples of quivers of wild type. I will discuss special mutations between these(strongly) exceptional collections and the AuslanderReiten triangles among them. Bumsig Kim, KIAS, Seoul, Korea Title: Logarithmic stable maps A new compactification of maps from curves, using only finite maps, will be presented, which is a joint work with A. Kresch and Y.G. Oh. After this, I will apply it to provide a modular desingularization of the main component of moduli of stable maps to any projective space. A notion of logarithmic stable maps will be needed for the purpose as well as the other general reason. Alexander Kuznetsov, Steklov Institute, Moscow, Russia Title: Exceptional collections on SGr(2,2n) and OGr(2,2n+1) I will use the notion of a Lefschetz exceptional collection to construct exceptional collections on SGr(2,2n) and OGr(2,2n+1)  the Grassmanians of 2dimensional subspaces isotropic for a symplectic form on a 2ndimensional vector space and for a quadratic form on a (2n+1)dimensional vector space respectively. Markus Perling 1, 2, RuhrUniversität, Bochum, Germany Title: Exceptional sequences of invertible sheaves on rational surfaces We present an easy procedure to construct exceptional and strongly exceptional sequences of invertible sheaves on smooth complete rational surfaces. We show that on every such surface there exists an exceptional sequence of invertible sheaves, and we give a criterion for the existence of full strongly exceptional sequences of this type. We present a complete classification of full strongly exceptional sequences of invertible sheaves for toric surfaces. Viktor Przhyalkowski, Steklov Institute, Moscow, Russia Title: Weak LandauGinzburg models of Fano varieties Mirror symmetry conjectures states that for any smooth Fano variety there exists a dual LandauGinzburg model, that is, a pencil of algebraic varieties whose symplectic properties transforms to algebraic ones of the initial Fano, and vice versa, whose algebraic properties transforms to symplectic ones. One of the basic problems of mirror symmetry is to find such models. We discuss a purely computational method of finding natural candidates for dual models (called weak LandauGinzburg models). We discuss their properties and their relations with toric degenerations. Atsushi Takahashi, Osaka University, Japan Title: Homological Mirror Symmetry for Cusp Singularities I will formulate and prove the Homological mirror symmetry conjecture for cusp singularities, the equivalence between the derived category of coherent sheaves on a weight projective line and the derived directed Fukaya category of a cusp singularity. Yokinobu Toda 1, IPMU, Kashiwa, Japan Title: Degenerations of del Pezzo surfaces (after Hacking, Prokhorov, Manetti) The Manetti surface is a complex surface with quotient singularities which admits a smoothing to the projective plane. I will give the classification of such surfaces. Suprisingly, Manetti surfaces are classified by the solution of Markov equation, which also appears in the theory of exceptional collections on the projective plane. This talk is an introduction to the paper of Hacking and Prokhorov, ``Degenerations of del Pezzo surfaces I, math.AG/0509529'' and Manetti, ''Normal degenerations of the complex plane, J. reine angew, Math. 419, 89118''. Yokinobu Toda 2, IPMU, Kashiwa, Japan Title:Stable pairs and wallcrossings in the derived category. The notion of stable pairs on CalabiYau 3folds and counting invariants of them are introduced by PandharipandeThomas. This is a variant of DonaldsonThomas theory, a kind of curve counting via coherent sheaves. In this talk I introduce new invariants which count certain stable perverse coherent sheaves, and show that they generalize PandharipandeThomas theory. Then I will show that the rationality conjecture of stable pair invarians is deduced from the wallcrossing phenomena of our new invariant. 