Higher-Dimensional Representations of the Reflection Equation Algebra

We consider a new method for constructing finite-dimensional irreducible representations of the reflection equation algebra. We construct a series of irreducible representations parameterized by Young diagrams. We calculate the spectra of central elements s _k=Tr_q L ^k of the reflection equation algebra on q-symmetric and q-antisymmetric representations. We propose a rule for decomposing the tensor product of representations into irreducible representations.     

Irreducible unitary representations of the groups U(p,q) sustaining passage to the limit aS q → ∞

The results of the note are inspired by the theory of representations of the infinite-dimensional classical groups. A new series of irreducible unitary representations of the group U(p,q) is described. These representations are constructed in the Gel'fand-Tsetlin basis and also as induced by nonunitary finite-dimensional representations of a maximal parabolic subgroup. As q they approximate irreducible unitary representations of the group U(p,).Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Akad. Nauk SSSR, Vol. 172, pp. 114–120, 1989.     

Strong Exceptional Sequences Provided by Quivers

Let Q be a finite quiver without oriented cycles. Denote by U (Q) the fine moduli space of stable thin sincere representations of Q with respect to the canonical stability notion. We prove Ext _(Q) ^l (U, U) = 0 for all l > 0 and compute the endomorphism algebra of the universal bundle U. Moreover, we obtain a necessary and sufficient condition for when this algebra is isomorphic to the path algebra of the quiver Q. If so, then the bounded derived categories of finitely generated right k Q-modules and that of coherent sheaves on (Q) are related via the full and faithful functor – _kQ ^L U.     

Genuine Representations of the Metaplectic Group

This paper determines the –correspondence for the dual pairs (O(p, q), Sp(2n, R)) when p+q=2n+1. As a consequence, there is a natural bijection between genuine irreducible representations of the metaplectic group Mp(2n, R) and irreducible representations of SO(p, q) with p+q=2n+1.     

On a cubic lifting

Let % MathType!End!2!1! be the three-fold cover of SL₂. We prove there is a lifting of the genuine automorphic representations of % MathType!End!2!1! to the automorphic representations of SL₂, using a relative trace formula. Partially supported by NSF DMS 9304580. Partially supported by NSF DMS 7209098.     

Rational Conformal Field Theory in Four Dimensions

We use the recently established rationality of correlation functions in a globally conformally invariant quantum field theory satisfying Wightman axioms to construct a family of solvable models in the four-dimensional Minkowski space–time. We consider the model of a neutral two-dimension scalar field in detail. It depends on a positive real parameter c, an analogue of the Virasoro central charge; for all (finite) c, it admits an infinite number of conserved symmetric tensor currents. The operator product algebra of coincides with a simpler one generated by a bilocal scalar field V(x ₁,x ₂) of dimension 1+1. The modes of V together with the unit operator span an infinite-dimensional Lie algebra _V , whose vacuum (i.e., zero-energy lowest-weight) representations depend only on the central charge c. The Wightman positivity (i.e., unitarity of the representations of _V ) is proved equivalent to c.     

Estimation of a K-Functional of Higher Order in Terms of a K-Functional of Lower Order

Let U _j be a finite system of functionals of the form , and let be the subspace of the Sobolev space , 1 p +, that consists only of functions g such that U _j(g) = 0 for k _j < r. It is assumed that there exists at least one jump _j for every function _j , and if _j = _s for j s, then k _j k _s. For the K-functional

On solutions of elliptic differential equations with operator coefficients

It is proved that on a simply connected region the solutions of the elliptic partial differential equation have representations U(x,y) = QV(x,y), where V admits local power series expansion in the "operator variable" xI + yI and (Q,T) forms a standard pair for the monic operator polynomial A₀ + A₁ + + ^s-1A_s-1 + ^sI.This paper was written while the autor was employed at the Vrije Universiteit in Amsterdam.     

RC *-fields

It is stated that if a Boolean family W of valuation rings of a field F satisfies the block approximation property (BAP) and a global analog of the Hensel-Rychlick property (THR), in which case F, W is called an RC^*-field, then F is regularly closed with respect to the family W (The-orem 1). It is proved that every pair F, W, where W is a weakly Boolean family of valuation rings of a field F, is embedded in the RC^*-field F₀, W₀ in such a manner that R₀ R₀ F, R₀ W₀ is a continuous map, W₀ is homeomorphic over W to a given Boolean space, and R₀ is a superstructure of R₀ F for every R₀ W₀ (Theorem 2).Translated fromAlgebra i Logika, Vol. 33, No. 4, pp. 367–386, July-August, 1994.     

Quasi-Shuffle Products

Given a locally finite graded set A and a commutative, associative operation on A that adds degrees, we construct a commutative multiplication * on the set of noncommutative polynomials in A which we call a quasi-shuffle product; it can be viewed as a generalization of the shuffle product III. We extend this commutative algebra structure to a Hopf algebra (U, *, ); in the case where A is the set of positive integers and the operation on A is addition, this gives the Hopf algebra of quasi-symmetric functions. If rational coefficients are allowed, the quasi-shuffle product is in fact no more general than the shuffle product; we give an isomorphism exp of the shuffle Hopf algebra (U, III, ) onto (U, *, ) the set L of Lyndon words on A and their images { exp(w) w L} freely generate the algebra (U, *). We also consider the graded dual of (U, *, ). We define a deformation *_q of * that coincides with * when q = 1 and is isomorphic to the concatenation product when q is not a root of unity. Finally, we discuss various examples, particularly the algebra of quasi-symmetric functions (dual to the noncommutative symmetric functions) and the algebra of Euler sums.     

Finite splitting fields of normal subgroups

Let G be a finite group, a normal subgroup, p a prime, a finite splitting field of characteristic p for G and We prove that is a splitting field for N, using the action of the Galois group of the field extension on the irreducible representations of N. As is a splitting field for the symmetric group S_n we get as a corollary that is a splitting field for the alternating group A_n. Received: 31 July 2003     

A representation theorem for weak automorphisms of a universal algebra

Given a group G and a descending chainG ₀,G ₁,...,G _n, of normal subgroups ofG, we prove that there exists a universal algebra , such that the chain ...W_n( )...W₁( }) W₀( )W( ) is isomorphic to the chain ...G _n ...G ₁G ₀G, where W( ) is the group of weak automorphisms of , and W_n( ) is the group of weak automorphisms of that leaves alln-ary operations fixed.We also prove that there are an infinite number of non-isomorphic algebras that satisfy the above.These results are a generalization of those proved by J. Sichler, in the special case when G=G₀, and G₁=G₂=...=G_n=....Presented by J. Mycielski.This paper comprises part of the author's doctoral dissertation at the University of Notre Dame in 1983. The author wishes to express her deep gratitude to Professor Abraham Goetz for suggesting this problem, for being extremely generous with his time and experience, and for giving her his constant encouragement. The author also thanks the reviewer for his helpful comments.     

The Lattice of Interpretability Types of Cantor Varieties

For integers 1 m < n, a Cantor variety with m basic n-ary operations _i and n basic m-ary operations _k is a variety of algebras defined by identities _k(₁( ), ... , _m( )) = _k and i(₁( ), ... ,_n( )) = y _i, where = (x ₁., ... , x _n) and = (y ₁, ... , y _m). We prove that interpretability types of Cantor varieties form a distributive lattice, , which is dual to the direct product ₁ × ₂ of a lattice, ₁, of positive integers respecting the natural linear ordering and a lattice, ₂, of positive integers with divisibility. The lattice is an upper subsemilattice of the lattice of all interpretability types of varieties of algebras.     

Locally homogeneous Riemannian manifolds and Cartan triples

Ann-dimensional Cartan triple is a triple (g, , ) consisting of a Lie subalgebra g of so(n) (endowed with the Killing form), a linear map : ⁿ g and a bilinear antisymmetric map ²( ⁿ , g), which together satisfy (1.25)–(1.28) of Section 1. LetM _n be the set ofmaximal n-dimensional Cartan triples, and letA _n be thenatural action of the orthogonal group O(n) onM _n (Section 3). One shows that there is a bijective mapping from the set of local isometry classes ofn-dimensional locally homogeneous Riemannian manifolds to the set of orbits ofA _n (Theorem 3.1(a)). Under this bijection, the classes of homogeneous Riemannian manifolds correspond to orbits ofclosed Cartan triples.     

Joint similarity problems and the generation of operator algebras with bounded length

There is a pair of commuting operators (T ₁,T ₂) on Hilbert space such that eachT ₁ andT ₂ is similar to a contraction but the pair (T ₁,T ₂) is not similar to a pair of contractions. There is a pair of commuting unitarizable representations (₁,₂) on the free group withN2 generators such that (₁,₂) is not similar to a pair of unitary representations. In connection with these examples, we introduce and study a notion of length for aC ^*-algebra (or an operator algebra) generated by two subalgebras, which is analogous to the minimum length of a word in the generators of a group.Partially supported by the N.S.F.     

Globally Irreducible Representations of Finite Groups and Integral Lattices

The notion of globally irreducible representations of finite groups has been introduced by B. H. Gross, in order to explain new series of Euclidean lattices discovered recently by N. Elkies and T. Shioda using Mordell--Weil lattices of elliptic curves. In this paper we first give a necessary condition for global irreducibility. Then we classify all globally irreducible representations of L ₂(q) and ²B₂(q), and of the majority of the 26 sporadic finite simple groups. We also exhibit one more globally irreducible representation, which is related to the Weil representation of degree (pⁿ-1)/2 of the symplectic group Sp_2n(p) (p 1 (mod 4) is a prime). As a consequence, we get a new series of even unimodular lattices of rank 2(pⁿ–1). A summary of currently known globally irreducible representations is given.     

The Spectral Function and Principal Eigenvalues for Schrödinger Operators

Let m , 0 m₊ in Kato's class. We investigate the spectral function s( + m) where s( + m) denotes the upper bound of the spectrum of the Schrödinger operator + m. In particular, we determine its derivative at 0. If m_- is sufficiently large, we show that there exists a unique ₁ > 0 such that s( + ₁m) = 0. Under suitable conditions on m⁺ it follows that 0 is an eigenvalue of + ₁m with positive eigenfunction.     

Degenerate Principal Series Representations of U(p, q) and Spin0(p, q)

Let p>q and let G be the group U(p, q) or Spin₀(p, q). Let P=LN be the maximal parabolic subgroup of G with Levi subgroup where

Kazhdan-Lusztig correspondence for the representation category of the triplet W-algebra in logarithmic CFT

To study the representation category of the triplet W-algebra that is the symmetry of the (1, p) logarithmic conformal field theory model, we propose the equivalent category C _p of finite-dimensional representations of the restricted quantum group Ū _q sℓ(2) at . We fully describe the category C _p by classifying all indecomposable representations. These are exhausted by projective modules and three series of representations that are essentially described by indecomposable representations of the Kronecker quiver. The equivalence of the -and Ū _q sℓ(2)-representation categories is conjectured for all p = 2 and proved for p = 2. The implications include identifying the quantum group center with the logarithmic conformal field theory center and the universal R-matrix with the braiding matrix. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 148, No. 3, pp. 398–427, September, 2006.     

Canonical representations on two-sheeted hyperboloids

The two-sheeted hyperboloid in ℝⁿ can be identified with the unit sphere Ω in ℝⁿ with the equator removed. Canonical representations of the group G = SO ₀(n − 1, 1) on are defined as the restrictions to G of the representations of the overgroup = SO ₀(n, 1) associated with a cone. They act on functions and distributions on the sphere Ω. We decompose these canonical representations into irreducible constituents and decompose the Berezin form. Bibliography: 12 titles. To the memory of my teacher F. A. Berezin __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 331, 2006, pp. 91–124.