Gelfand�CTsetlin algebras and cohomology rings of Laumon spaces

Laumon moduli spaces are certain smooth closures of the moduli spaces of maps from the projective line to the flag variety of GL _n . We calculate the equivariant cohomology rings of the Laumon moduli spaces in terms of Gelfand–Tsetlin subalgebra of U(gl _n ) and formulate a conjectural answer for the small quantum cohomology rings in terms of certain commutative shift of argument subalgebras of U(gl _n ).     

Characters of representations of the quantum toroidal algebra : Plane partitions with “stands”

An expression for the generating function of plane partitions a _i,j subject to the constraints a _m,n = 0 and a _i,j ? k _j , 1 ? j ? n, which is the character of an irreducible representation of the quantum toroidal algebra , is obtained.     

Quantum actions on discrete quantum spaces and a generalization of Clifford’s theory of representations

To any action of a compact quantum group on a von Neumann algebra which is a direct sum of factors we associate an equivalence relation corresponding to the partition of a space into orbits of the action. We show that in case all factors are finite-dimensional (i.e., when the action is on a discrete quantum space) the relation has finite orbits. We then apply this to generalize the classical theory of Clifford, concerning the restrictions of representations to normal subgroups, to the framework of quantum subgroups of discrete quantum groups, itself extending the context of closed normal quantum subgroups of compact quantum groups. Finally, a link is made between our equivalence relation in question and another equivalence relation defined by R. Vergnioux.     

Integrably asymptotic affine homeomorphisms of the circle and Teichmüller spaces

A quasisymmetric homeomorphism of the unit circle S¹ is called integrably asymptotic affine if it admits a quasiconformal extension into the unit disk so that its complex dilatation is square integrable in the Poincaré metric on the unit disk. Let QS_* (s¹) be the space of such maps. Here we give some characterizations and properties of maps in QS_* (S¹). We also show that QS_* (S₁)/M?b (S¹) is the completion of Diff(S¹)/M?b(S₁) in the Weil-Petersson metric.     

Integrably asymptotic affine homeomorphisms of the circle and Teichmüller spaces

A quasisymmetric homeomorphism of the unit circle S1 is called integrably asymptotic affine if it admits a quasiconformal extension into the unit disk so that its complex dilatation is square integrable in the Poincar metric on the unit disk. Let QS*(S1) be the space of such maps. Here we give some characterizations and properties of maps in QS(S1). We also show that QS*(S1)/M(O)b(S1) is the completion of Diff(S1)/M(O)b(S1) in the Weil-Petersson metric.     

A general form of Gelfand�CKazhdan criterion

We formalize the notion of matrix coefficients for distributional vectors in a representation of a real reductive group, which consist of generalized functions on the group. As an application, we state and prove a Gelfand?CKazhdan criterion for a real reductive group in very general settings.     

Analogue Zhelobenko invariants, Bernstein–Gelfand–Gelfand operators and the Kostant Clifford algebra conjecture

Let $ \mathfrak{g} $ be a complex simple Lie algebra. The Kostant Clifford algebra conjecture can be formulated and somewhat extended as a question [7, Conj. 1.3] concerning the Harish-Chandra map for the enveloping algebra of $ \mathfrak{g} $ . In that work [7, Cor. 8.8] an analogue Kostant conjecture, obtained by replacing the Harish-Chandra map by a ??generalized Harish-Chandra?? map, was proved using a careful analysis of Zhelobenko invariants which describe the image of this map. In the present work we establish [7, Conj. 1.3] by showing that there are analogue Zhelobenko invariants which describe the image of the Harish-Chandra map. Following this a similar proof to that of [7, Cor. 8.8] goes through. In the last section a rather precise form of the Kostant Clifford algebra conjecture is established.     

P-twisted affine Lie algebra and its realizations by twisted vertex operators

In this paper, we define a P-twisted affine Lie algebra, and construct its realizations by twisted vertex operators.     

Asymptotics of random lozenge tilings via Gelfand–Tsetlin schemes

A Gelfand–Tsetlin scheme of depth \(N\) is a triangular array with \(m\) integers at level \(m\) , \(m=1,\ldots ,N\) , subject to certain interlacing constraints. We study the ensemble of uniformly random Gelfand–Tsetlin schemes with arbitrary fixed \(N\) th row. We obtain an explicit double contour integral expression for the determinantal correlation kernel of this ensemble (and also of its \(q\) -deformation). This provides new tools for asymptotic analysis of uniformly random lozenge tilings of polygons on the triangular lattice; or, equivalently, of random stepped surfaces. We work with a class of polygons which allows arbitrarily large number of sides. We show that the local limit behavior of random tilings (as all dimensions of the polygon grow) is directed by ergodic translation invariant Gibbs measures. The slopes of these measures coincide with the ones of tangent planes to the corresponding limit shapes described by Kenyon and Okounkov (Acta Math 199(2):263–302, 2007). We also prove that at the edge of the limit shape, the asymptotic behavior of random tilings is given by the Airy process. In particular, our results cover the most investigated case of random boxed plane partitions (when the polygon is a hexagon).     

Δ-graphs of polytopes in Bruns and Gubeladze K-theory

W. Bruns and J. Gubeladze introduced a new version of algebraic K-theory where K-groups are additionally parameterized by polytopes of some type. In this paper we propose a concept of stable E-equivalence which can be used to calculate K-groups for high-dimensional polytopes. Polytopes which are stable E-equivalent have similar inner structures and isomorphic K-groups. In addition, for each polytope we define a Δ-graph which is an oriented graph being invariant under a stable E-equivalence.     

A characterization of Haj?asz-Sobolev and Triebel-Lizorkin spaces via grand Littlewood-Paley functions

In this paper, we establish the equivalence between the Haj?asz-Sobolev spaces or classical Triebel-Lizorkin spaces and a class of grand Triebel-Lizorkin spaces on Euclidean spaces and also on metric spaces that are both doubling and reverse doubling. In particular, when p∈(n/(n+1),∞), we give a new characterization of the Haj?asz-Sobolev spaces via a grand Littlewood-Paley function.     

Symmetric chains,Gelfand–Tsetlin chains,and the Terwilliger algebra of the binary Hamming scheme

The de Bruijn–Tengbergen–Kruyswijk (BTK) construction is a simple algorithm that produces an explicit symmetric chain decomposition of a product of chains. We linearize the BTK algorithm and show that it produces an explicit symmetric Jordan basis (SJB). In the special case of a Boolean algebra, the resulting SJB is orthogonal with respect to the standard inner product and, moreover, we can write down an explicit formula for the ratio of the lengths of the successive vectors in these chains (i.e., the singular values). This yields a new constructive proof of the explicit block diagonalization of the Terwilliger algebra of the binary Hamming scheme. We also give a representation theoretic characterization of this basis that explains its orthogonality, namely, that it is the canonically defined (up to scalars) symmetric Gelfand–Tsetlin basis.     

Some extensions of the Levi�CCivit�� functional equation and richly periodic spaces of functions

We study some classes of functional equations using geometric results on orbits for infinite-dimensional continuous representations of groups. One of the typical results is the following. Let G be a connected topological group. Suppose that continuous functions a _i , b _i , u _i , v _i on G satisfy the condition $$\sum_{i=1}^ma_i(g)b_i(hg) = \sum_{i=1}^n u_i(g)v_i(h), \qquad \forall g,h \in G.$$ If the functions a ₁, ... , a _m are linearly independent then all b _i are matrix elements of a continuous finite-dimensional representation of G. For ${G = \mathbb{R}^n}$ this means that b _i are quasipolynomials.     

On the sharpness of Bruen’s bound for intersection sets in Desarguesian affine spaces

In this note we investigate the sharpness of Bruen’s bound on the size of a t-fold blocking set in \(AG(n,q)\) with respect to the hyperplanes. We give a construction for t-fold blocking sets meeting Bruen’s bound with \(t=q-n+2\) . This construction is used further to find the minimal size of a t-fold affine blocking set with \(t=q-n+1\) . We prove that for blocking sets in the geometries \(AG(n,2)\) the difference between the size of an optimal t-fold blocking set and tn exceeds any given number. In particular, we deviate infinitely from Bruen’s bound as n goes to infinity. We conclude with a construction that gives t-fold blocking sets with \(t=q-n+3\) whose size is close to the lower bounds known so far.