Browsing 1 - Oberwolfach Preprints (OWP) by Title
Now showing items 241-260 of 407
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On a Cheeger Type Inequality in Cayley Graphs of Finite Groups
[OWP-2019-20] (Mathematisches Forschungsinstitut Oberwolfach, 2019-07-22) - (7 July - 7 October 2017)Let $G$ be a finite group. It was remarked by Breuillard-Green-Guralnick-Tao that if the Cayley graph $C(G,S)$ is an expander graph and is non-bipartite then the spectrum of the adjacency operator $T$ is bounded away from ... -
On a Conjecture of Khoroshkin and Tolstoy
[OWP-2022-14] (Mathematisches Forschungsinstitut Oberwolfach, 2022-08-02)We prove a no-go theorem on the factorization of the lower triangular part in the Gaussian decomposition of the Yangian's universal $R$-matrix, yielding a negative answer to a conjecture of Khoroshkin and Tolstoy from ... -
On a Group Functor Describing Invariants of Algebraic Surfaces
[OWP-2019-08] (Mathematisches Forschungsinstitut Oberwolfach, 2019-03-01)Liedtke (2008) has introduced group functors $K$ and $\tilde K$, which are used in the context of describing certain invariants for complex algebraic surfaces. He proved that these functors are connected to the theory of ... -
On an Effective Variation of Kronecker’s Approximation Theorem Avoiding Algebraic Sets
[OWP-2017-28] (Mathematisches Forschungsinstitut Oberwolfach, 2017-10-19)Let $\Lambda \subset \mathbb R^n$ be an algebraic lattice, coming from a projective module over the ring of integers of a number field $K$. Let $\mathcal Z \subset \mathbb R^n$ be the zero locus of a finite collection of ... -
On Canonical Forms for Two-person Zero-sum Limit Average Payoff Stochastic Games
[OWP-2011-35] (Mathematisches Forschungsinstitut Oberwolfach, 2011-05-29)We consider two-person zero-sum mean payoff undiscounted stochastic games. We give a sufficient condition for the existence of a saddle point in uniformly optimal stationary strategies. Namely, we obtain sufficient ... -
On Co-Minimal Pairs in Abelian Groups
[OWP-2019-19] (Mathematisches Forschungsinstitut Oberwolfach, 2019-07-09)A pair of non-empty subsets $(W,W')$ in an abelian group $G$ is a complement pair if $W+W'=G$. $W'$ is said to be minimal to $W$ if $W+(W'\setminus \{w'\}) \neq G, \forall \,w'\in W'$. In general, given an arbitrary subset ... -
On commuting varieties of nilradicals of Borel subalgebras of reductive Lie algebras
[OWP-2012-14] (Mathematisches Forschungsinstitut Oberwolfach, 2012-12-04)Let $G$ be a connected reductive algebraic group defined over an algebraically closed field $\mathbb{k}$ of characteristic zero. We consider the commuting variety $\mathcal{C}(\mathfrak{u})$ of the nilradical $\mathfrak{u}$ ... -
On Concentrators and Related Approximation Constants
[OWP-2013-14] (Mathematisches Forschungsinstitut Oberwolfach, 2013-06-10)Pippenger ([Pip77]) showed the existence of (6m, 4m, 3m, 6)-concentrator for each positive integer m using a probabilistic method. We generalize his approach and prove existence of (6m, 4m, 3m, 5.05)-concentrator (which ... -
On conjugacy of MASAs and the outer automorphism group of the Cuntz algebra
[OWP-2013-21] (Mathematisches Forschungsinstitut Oberwolfach, 2013-10-29)We investigate the structure of the outer automorphism group of the Cuntz algebra and the closely related problem of conjugacy of MASAa in $\mathcal{O}_n$. In particular, we exhibit an uncountable family of MASAs, conjugate ... -
On densities of lattice arrangements intersecting every i-dimensional affine subspace
[OWP-2016-08] (Mathematisches Forschungsinstitut Oberwolfach, 2016-05-10)In 1978, Makai Jr. established a remarkable connection between the volume-product of a convex body, its maximal lattice packing density and the minimal density of a lattice arrangement of its polar body intersecting every ... -
On Dykstra’s Algorithm with Bregman Projections
[OWP-2024-04] (Mathematisches Forschungsinstitut Oberwolfach, 2024-04-16)We provide quantitative results on the asymptotic behavior of Dykstra’s algorithm with Bregman projections, a combination of the well-known Dykstra’s algorithm and the method of cyclic Bregman projections, designed to find ... -
On Generalizations of Kac-Moody Groups
[OWP-2010-06] (Mathematisches Forschungsinstitut Oberwolfach, 2010-03-10)In [7] we define a Curtis-Tits group as a certain generalization of a Kac-Moody group. We distinguish between orientable and non-orientable Curtis-Tits groups and identify all orientable Curtis-Tits groups as Kac-Moody ... -
On Local Combinatorial Formulas for Chern Classes of Triangulated Circle Bundle
[OWP-2016-16] (Mathematisches Forschungsinstitut Oberwolfach, 2016-08-17)Principal circle bundle over a PL polyhedron can be triangulated and thus obtains combinatorics. The triangulation is assembled from triangulated circle bundles over simplices. To every triangulated circle bundle over a ... -
On Overgroups of Distinguished Unipotent Elements in Reductive Groups and Finite Groups of Lie Type
[OWP-2024-05] (Mathematisches Forschungsinstitut Oberwolfach, 2024-06-18)Suppose G is a simple algebraic group defined over an algebraically closed field of good characteristic p. In 2018 Korhonen showed that if H is a connected reductive subgroup of G which contains a distinguished unipotent ... -
On periodic solutions and global dynamics in a periodic differential delay equation
[OWP-2014-08] (Mathematisches Forschungsinstitut Oberwolfach, 2014-05-13)Several aspects of global dynamics and the existence of periodic solutions are studied for the scalar differential delay equation $x'(t) = a(t)f(x([t-K]))$, where $f(x)$ is a continuous negative feedback function, $x \cdot ... -
On Reflection Subgroups of Finite Coxeter Groups
[OWP-2011-06] (Mathematisches Forschungsinstitut Oberwolfach, 2011-05-9)Let $W$ be a finite Coxeter group. We classify the reflection subgroups of $W$ up to conjugacy and give necessary and sufficient conditions for the map that assigns to a reflection subgroup $R$ of $W$ the conjugacy class ... -
On Residuals of Finite Groups
[OWP-2019-17] (Mathematisches Forschungsinstitut Oberwolfach, 2019-05-28)A theorem of Dolfi, Herzog, Kaplan, and Lev [DHKL07, Thm. C] asserts that in a finite group with trivial Fitting subgroup, the size of the soluble residual of the group is bounded from below by a certain power of the group ... -
On Selfinjective Artin Algebras Having Generalized Standard Quasitubes
[OWP-2010-18] (Mathematisches Forschungsinstitut Oberwolfach, 2010-03-18)We give a complete description of the Morita equivalence classes of all connected selfinjective artin algebras for which the Auslander-Reiten quiver admits a family of quasitubes having common composition factors, closed ... -
On Siegel modular forms of level p and their properties mod p
[OWP-2009-23] (Mathematisches Forschungsinstitut Oberwolfach, 2009-03-16)Using theta series we construct Siegel modular forms of level p which behave well modulo $p$ in all cusps. This construction allows us to show (under a mild condition) that all Siegel modular forms of level p and weight 2 ... -
On test sets for nonlinear integer maximization
[OWP-2007-05] (Mathematisches Forschungsinstitut Oberwolfach, 2007-03-23)A finite test set for an integer maximation problem enables us to verify whether a feasible point atains the global maximum. We establish in this paper several general results that apply to integer maximization problems ...