Existence of Klyachko Models for GL(n;R) and GL(n;C)
We prove that any unitary representation of GL(n;R) and GL(n;C) admits an equivariant linear form with respect to one of the subgroups considered by Klyachko.
math.RT↗
arXiv subjects
Siddhartha Sahi
Publications and source records attributed to Siddhartha Sahi.
Equivariant cohomology and tensor categories
We propose the notion of a supercategory as an alternative approach to supermathematics. We show that this setting is rich to carry out many of the basic constructions of supermathematics. We also prove generalizations of a number of results in equivariant cohomology, including the Chern-Weil theorem for an arbitrary rigid Lie algebra object. For a quadratic Lie algebra object we obtain a proof of the Duflo isomorphism along the lines of Alekseev-Meinrenken, thereby generalizing their result to Lie superalgebras.
math.QA↗
Biorthogonal Expansion of Non-Symmetric Jack Functions
We find a biorthogonal expansion of the Cayley transform of the non-symmetric Jack functions in terms of the non-symmetric Jack polynomials, the coefficients being Meixner-Pollaczek type polynomials. This is done by computing the Cherednik-Opdam transform of the non-symmetric Jack polynomials multiplied by the exponential function.
math.CA↗
Raising and Lowering Operators for Askey-Wilson Polynomials
In this paper we describe two pairs of raising/lowering operators for Askey-Wilson polynomials, which result from constructions involving very different techniques. The first technique is quite elementary, and depends only on the ''classical'' properties of these polynomials, viz. the q-difference equation and the three term recurrence. The second technique is less elementary, and involves the one-variable version of the double affine Hecke algebra.
math.QA↗
Triple groups and Cherednik algebras
The goal of this paper is to define a new class of objects which we call triple groups and to relate them with Cherednik's double affine Hecke algebras. This has as immediate consequences new descriptions of double affine Weyl and Artin groups, the double affine Hecke algebras as well as the corresponding elliptic objects. From the new descriptions we recover results of Cherednik on automorphisms of double affine Hecke algebras.
math.QA↗
Explicit Hilbert spaces for certain unipotent representations III
We consider the groups G which arise from real semisimple Jordan algebras via the Tits-Koecher-Kantor construction. Such a G is characterized by the fact that it admits a parabolic subgroup P=LN which is conjugate to its opposite, and for which the nilradical N is abelian. In this situation, the Levi component L has a finite number of orbits on N; and each orbit carries a measure which transforms by a character under L. By Mackey theory the space of L2-functions on each orbit carries a natural irreducible unitary representation of P, and we consider the following two problems: (1) Extend this representation of P to a unitary representation of G. (2) Decompose tensor products of the resulting representations.
math.RT↗
Convolution of invariant distributions: Proof of the Kashiwara-Vergne conjecture
Consider the Kontsevich $\star$-product on the symmetric algebra of a finite dimensional Lie algebra $\mathfrak g$, regarded as the algebra of distributions with support 0 on $\mathfrak g$. In this paper, we extend this $\star$-product to distributions satisfying an appropriate support condition. As a consequence, we prove a long standing conjecture of Kashiwara-Vergne on the convolution of germs of invariant distributions on the Lie group $G$.
math.QA↗
Kontsevich quantization and invariant distributions on Lie groups
We study Kontsevich's deformation quantization for the dual of a finite-dimensional real Lie algebra (or superalgebra) g. In this case the Kontsevich star-product defines a new convolution on S(g), regarded as the space of distributions supported at 0 in g. For p in S(g), we show that the convolution operator f->f*p is a differential operator with analytic germ. We use this fact to prove a conjecture of Kashiwara and Vergne on invariant distributions on a Lie group. This yields a new proof of Duflo's result on local solvability of bi-invariant differential operators on a Lie group. Moreover, this new proof extends to Lie supergroups.
math.QA↗
Deformation quantization and invariant distributions
In 1979, M. Kashiwara and M. Vergne formulated a conjecture on a Lie group G which implies that the Duflo isomorphism of Z(g) and S(g)^g extends to a natural module isomorphism between the spaces of germs of invariant distributions on G and g=Lie(G), respectively. They also proved their conjecture for G solvable. Using Kontsevich's deformation quantization we establish directly this result for distributions on any real Lie group G. In turn this gives a new proof of Duflo's result on the local solvability of bi-invariant differential operators on G.
math.QA↗
Nonsymmetric Koornwinder polynomials and duality
Motivated by the work of Koornwinder, Macdonald, Cherednik, Noumi, and van Diejen we define a 6-parameter double affine Hecke algebra and establish its basic structural properties, including the existence of an involution. We relate the algebra to (symmetric and nonsymmetric) Koornwinder polynomials via the method of intertwiners and, as a consequence, obtain a proof of Macdonald's duality conjecture for Koornwinder polynomials. Combined with earlier work of van Diejen this completely settles all the outstanding conjectures of Macdonald and Koornwinder about these polynomials.
q-alg↗
Explicit Hilbert spaces for certain unipotent representations II
We construct an explicit realization of a minimal representation of G, where G is the conformal group of a real Jordan algebra N. We characterize spherical vectors for these representation and prove that they are closely related to the Bessel K-function $K_τ(z)$. The resulting construction can be used to study tensor powers of the minimal representation and establish an extension of the Howe duality correspondence to some exceptional groups.
math.RT↗
Tensor products of singular representations and an extension of the theta-correspondence
In this paper we consider the problem of decomposing tensor products of certain singular unitary representations of a semisimple Lie group G. Using explicit models for these representations (constructed earlier by one of us) we show that the decomposition is controlled by a reductive homogeneous space G'/H'. Our procedure establishes a correspondence between certain unitary representations of G and those of G'. This extends the usual theta--correspondence for dual reductive pairs. As a special case we obtain a correspondence between certain representations of real forms of E_7 and F_4.
math.RT↗
A new formula for weight multiplicities and characters
We describe a new formula for weight multiplicities and characters of semisimple Lie algebras. Our formula expresses these weight multiplicities as sums of positive rational numbers. In fact, the formula works more generally for the Jacobi polynomials of Heckman and Opdam, which are a one parameter deformation of these characters. As a consequence we prove that after suitable normalization, the coefficients of these polynomials are themselves polynomials in the parameter with positive integral coefficients. This generalizes our earlier joint work with F. Knop on Jack polynomials.
math.QA↗
The binomial formula for nonsymmetric Macdonald polynomials
Inhomogeneous analogues of symmetric and nonsymmetric Macdonald polynomials were introduced by F. Knop and the author. In the symmetric case A. Okounkov has recently proved a beautiful expansion formula which can be viewed as a multivariable generalization of the q-binomial theorem. It is becoming clear that many interesting results in the symmetric setting can also be established in the nonsymmetric setting. In this paper, we prove the nonsymmetric analogue the binomial formula, and also discuss the limiting case of Jack polynomials.
q-alg↗
A recursion and a combinatorial formula for Jack polynomials
Heckman and Opdam introduced a non-symmetric analogue of Jack polynomials using Cherednik operators. In this paper, we derive a simple recursion formula for these polynomials and formulas relating the symmetric Jack polynomials with the non-symmetric ones. These formulas are then implemented by a closed expression of symmetric and non-symmetric Jack polynomials in terms of certain tableaux. The main application is a proof of a conjecture of Macdonald stating certain integrality and positivity properties of Jack polynomials.
q-alg↗
Difference equations and symmetric polynomials defined by their zeros
In this paper, we introduce a new family of symmetric polynomials which depends on a parameter r. They are defined by specifying certain of their zeros. For the parameter values 1/2, 1, and 2 they have an interpretation in terms of Capelli identities. First, we give explicit formulas in some special cases. Then we show that the polynomials can also be defined in terms of difference equations. As a corollary we obtain that their top homogeneous part is a Jack polynomial. This is used to give a new proof of the Pieri formula for Jack polynomials.
q-alg↗
A new scalar product for nonsymmetric Jack polynomials
Symmetric Jack polynomials arise naturally in several contexts, including statistics, physics, combinatorics, and representation theory. They are pairwise orthogonal with repsect to two different inner products, the first defined by integration over an n-dimensional torus, and the second defined via a power series expansion. The nonsymmetric analogs of Jack polynomials were recently defined by Opdam via the first inner product. In this paper we show that they are also orthogonal with respect to an analog of the second product which was proposed by Dunkl. We also derive an explict formula for their norms.
q-alg↗