• On a Cheeger Type Inequality in Cayley Graphs of Finite Groups 

      [OWP-2019-20] Biswas, Arindam (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] Appel, Andrea; Gautam, Sachin; Wendlandt, Curtis (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] Dietrich, Heiko; Moravec, Primož (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] Fukshansky, Lenny; German, Oleg; Moshchevitin, Nikolay (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] Boros, Endre; Elbassioni, Khaled; Gurvich, Vladimir; Makino, Kazuhisa (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] Biswas, Arindam; Saha, Jyoti Prakash (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] Goodwin, Simon M.; Röhrle, Gerhard (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] Bondarenko, A. V.; Prymak, A.; Radchenko, D. (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] Conti, Roberto; Hong, Jeong Hee; Szymański, Wojciech (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] González Merino, Bernardo; Henze, Matthias (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] Pinto, Pedro; Pischke, Nicholas (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] Blok, Rieuwert J.; Hoffman, Corneliu (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] Mnev, Nikolai; Sharygin, Georgy (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] Bate, Michael; Böhm, Sören; Martin, Benjamin; Röhrle, Gerhard (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] Ivanov, Anatoli F.; Trofimchuk, Sergei I. (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] Douglass, J. Matthew; Pfeiffer, Götz; Röhrle, Gerhard (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] Aivazidis, Stefanos; Müller, Thomas (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] Karpicz, Maciej; Skowroński, Andrzej; Yamagata, Kunio (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] Böcherer, Siegfried; Nagaoka, Shoyu (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] Lee, Jon; Onn, Shmuel; Weismantel, Robert (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 ...