Browsing by Author "Buchweitz, Ragnar-Olaf"

Now showing 1 - 5 of 5
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    A McKay Correspondence for Reflection Groups
    (Oberwolfach : Mathematisches Forschungsinstitut Oberwolfach, 2018) Buchweitz, Ragnar-Olaf; Faber, Eleonore; Ingalls, Colin
    We construct a noncommutative desingularization of the discriminant of a finite reflection group G as a quotient of the skew group ring A=S∗G. If G is generated by order two reflections, then this quotient identifies with the endomorphism ring of the reflection arrangement A(G) viewed as a module over the coordinate ring SG/(Δ) of the discriminant of G. This yields, in particular, a correspondence between the nontrivial irreducible representations of G to certain maximal Cohen--Macaulay modules over the coordinate ring SG/(Δ). These maximal Cohen--Macaulay modules are precisely the nonisomorphic direct summands of the coordinate ring of the reflection arrangement A(G) viewed as a module over SG/(Δ). We identify some of the corresponding matrix factorizations, namely the so-called logarithmic co-residues of the discriminant.
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    Hochschild Cohomology in Algebra, Geometry, and Topology
    (Zürich : EMS Publ. House, 2016) Buchweitz, Ragnar-Olaf; Lowen, Wendy
    In 1945 Gerhard Hochschild published "On the cohomology groups of an associative algebra" in the Annals of Mathematics and thereby created what is now called Hochschild theory. In 1963, Murray Gerstenhaber proved that the Hochschild cohomology of any associative algebra carries a super-Poisson algebra structure, comprised of a graded commutative cup product and an odd super Lie algebra structure that acts through graded derivations with respect to the product. Subsequently, a number of higher structures have been discovered, and a vast body of research concerning and/or using Hochschild theory has developed in many different fields in mathematics and physics.
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    On the derived category of Grassmannians in arbitrary characteristic
    (Oberwolfach : Mathematisches Forschungsinstitut Oberwolfach, 2013) Buchweitz, Ragnar-Olaf; Leuschke, Graham J.; Van den Bergh, Michel
    In this paper we consider Grassmannians in arbitrary characteristic. Generalizing Kapranov's well-known characteristic-zero results we construct dual exceptional collections on them (which are however not strong) as well as a tilting bundle. We show that this tilting bundle has a quasi-hereditary endomorphism ring and we identify the standard, costandard, projective and simple modules of the latter.
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    Swallowtail on the shore
    (Oberwolfach : Mathematisches Forschungsinstitut Oberwolfach gGmbH, 2014) Buchweitz, Ragnar-Olaf; Faber, Eleonore
    Platonic solids, Felix Klein, H.S.M. Coxeter and a flap of a swallowtail: The five Platonic solids tetrahedron, cube, octahedron, icosahedron and dodecahedron have always attracted much curiosity from mathematicians, not only for their sheer beauty but also because of their many symmetry properties. In this snapshot we will start from these symmetries, move on to groups, singularities, and finally find the connection between a tetrahedron and a “swallowtail”. Our running example is the tetrahedron, but every construction can be carried out with any other of the Platonic solids.
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    The Magic Square of Reflections and Rotations
    (Oberwolfach : Mathematisches Forschungsinstitut Oberwolfach, 2018) Buchweitz, Ragnar-Olaf; Faber, Eleonore; Ingalls, Colin
    We show how Coxeter's work implies a bijection between complex reflection groups of rank two and real reflection groups in 0(3). We also consider this magic square of reflections and rotations in the framework of Clifford algebras: we give an interpretation using (s)pin groups and explore these groups in small dimensions.