Browsing FACULTY OF ARTS by Author "Hoffmann, Norbert"
Now showing items 120 of 21

The BodenHu conjecture holds precisely up to rank eight (Prepublished version)
Hoffmann, Norbert (Springer Verlag, 2004) 
The Brauer group of moduli spaces of vector bundles over a real curve
Hoffmann, Norbert; Indranil, Biswas; Amit, Hogadi; Schmitt, Alexander H.W. (American Mathematical Society (AMS), 2011)Let X be a geometrically connected smooth projective curve of genus gX ≥ 2 over R. Let M(r, ξ) be the coarse moduli space of geometrically stable vector bundles E over X of rank r and determinant ξ, where ξ is a real point ... 
EinsteinHermitian connection on twisted Higgs bundles (Prepublished Version)
Biswas, Indranil; Gómez, Tomás L.; Hoffmann, Norbert; Hogadi, Amit (Elsevier Masson, 2010)Let X be a smooth projective variety over C. We prove that a twisted Higgs vector bundle (E , θ) on X admits an Einstein–Hermitian connection if and only if (E , θ) is polystable. A similar result for twisted vector bundles ... 
Generalized vector bundles on curves (Prepublished version)
Hoffmann, Norbert; Stuhler, Ulrich; Jahnel, Joerg (de Gruyter, 1998)In their paper [14] G. Harder and M.S. Narasimhan (and independently D. Quillen) have constructed a canonical flag of subbundles on any vector bundle on a complete smooth algebraic curve over a field. This flag measures ... 
Homological algebra with locally compact abelian groups (Prepublished Version)
Hoffmann, Norbert; Spitzweck, Markus (Elsevier, 2007)In this article we study locally compact abelian (LCA) groups from the viewpoint of derived categories, using that their category is quasiabelian in the sense of J.P. Schneiders. We deﬁne a wellbehaved derived Homcomplex ... 
Independent parameters for special instanton bundles on P^{2n+1} (Prepublished Version)
Hoffmann, Norbert (Elsevier, 2011)Motivated by YangMills theory in 4n dimensions, and generalizing the notion due to Atiyah, Drinfeld, Hitchin and Manin for n = 1, Okonek, Spindler and Trautmann introduced instanton bundles and special instanton bundles ... 
The line on moduli stacks of principal bundles on a curve
Hoffmann, Norbert; Biswas, Indranil (Documenta Mathematica, 2010)Let G be an affine reductive algebraic group over an algebraically closed field k. We determine the Picard group of the moduli stacks of principal G–bundles on any smooth projective curve over k. 
Moduli schemes of generically simple Azumaya modules
Hoffmann, Norbert; Stuhler, Ulrich (Documenta Mathematica, 2005)Let A be an Azumaya algebra over a smooth projective variety X or more generally, a torsion free coherent sheaf of algebras over X whose generic fiber is a central simple algebra. We show that generically simple torsion ... 
The moduli stack of vector bundles on a curve (Prepublished Version)
Hoffmann, Norbert (Ramanujan Mathematical Society, 2010)This expository text tries to explain brie y and not too technically the notions of stack and algebraic stack, emphasizing as an example the moduli stack of vector bundles on an algebraic curve. 
Moduli stacks of vector bundles on curves and the King–Schofield rationality proof (Prepublished version)
Hoffmann, Norbert (Springer, 2010)Let C be a connected smooth projective curve of genus g ≥ 2 over an algebraically closed field k. Consider the coarse moduli scheme Bunr,d (resp. Bunr,L) of stable vector bundles on C with rank r and degree d ∈ Z (resp. ... 
New examples of stable bundles on CalabiYau threefolds (Prepublished Version)
Hoffmann, Norbert; Andreas, Björn (Oxford University Press, 2012)In this paper we present a construction of stable bundles on CalabiYau threefolds using the method of bundle extensions. This construction applies to any given CalabiYau threefold with h1 , 1 > 1. We give examples ... 
On moduli stacks of Gbundles over a curve (Prepublished version)
Hoffmann, Norbert (Springer, 2010)Let C be a smooth projective curve over an algebraically closed eld k of arbitrary characteristic. Given a linear algebraic group G over k, let MG be the moduli stack of principal Gbundles on C. We determine the set of ... 
On semistable vector bundles over curves (Prepublished version)
Hoffmann, Norbert; Biswas, Indranil; Hein, Georg (Elsevier, 2008)Let X be a geometrically irreducible smooth projective curve de ned over a eld k, and let E be a vector bundle on X. Then E is semistable if and only if there is a vector bundle F on X such that Hi(X; F E) = 0 for i = 0; ... 
The Picard group of a coarse moduli space of vector bundles in positive characteristic (Prepublished version)
Hoffmann, Norbert (Versita, copublished with Springer Verlag., 2012)Let C be a smooth projective curve over an algebraically closed field of arbitrary characteristic. Let Mss r,L denote the projective coarse moduli scheme of semistable rank r vector bundles over C with fixed determinant ... 
Poincaré families and automorphisms of principal bundles on a curve (Prepublished version)
Hoffmann, Norbert; Biswas, Indranil (Elsevier, 2009)Let C be a smooth projective curve, and let G be a reductive algebraic group. We give a necessary condition, in terms of automorphism groups of principal Gbundles on C, for the existence of Poincaré families parameterized ... 
Poincaré families of Gbundles on a curve (Prepublished version)
Hoffmann, Norbert; Biswas, Indranil (Springer Verlag, 2012)Let G be a reductive group over an algebraically closed ﬁeld k. Consider the moduli space of stable principal Gbundles on a smooth projective curve C over k. We give necessary and suﬃcient conditions for the existence of ... 
Rationality and Poincaré families for vector bundles with extra structure on a curve (Prepublished version)
Hoffmann, Norbert (Oxford University Press, 2007)Iterated Grassmannian bundles over moduli stacks of vector bundles on a curve are shown to be birational to an affine space times a moduli stack of degree 0 vector bundles, following the method of King and Schofield. ... 
Some moduli stacks of symplectic bundles on a curve are rational (Prepublished version)
Biswas, Indranil; Hoffmann, Norbert (Elsevier, 2008)Let C be a smooth projective curve of genus g ≥ 2 over a ﬁeld k. Given a line bundle L on C, let Sympl2n,L be the moduli stack of vector bundles E of rank 2n on C endowed with a nowhere degenerate symplectic form b : E ⊗ ... 
Stability of Arakelov bundles and tensor products without global sections
Hoffmann, Norbert (Documenta Mathematica, 2003)This paper deals with Arakelov vector bundles over an arithmetic curve, i.e. over the set of places of a number field. The main result is that for each semistable bundle E, there is a bundle F such that E⊗F has at least ... 
SU(5) heterotic standard model bundles (Prepublished version)
Hoffmann, Norbert; Andreas, Björn (Springer Verlag, 2012)We construct a class of stable SU(5) bundles on an elliptically ﬁbered CalabiYau threefold with two sections, a variant of the ordinary Weierstrass ﬁbration, which admits a free involution. The bundles are invariant under ...