arXiv subjects

A. U. Klimyk

Publications and source records attributed to A. U. Klimyk.

At least 19 recordsLinked to original sources

arXiv2007

Classification theorem on irreducible representations of the q-deformed algebra U'_q(so(n))

The aim of this paper is to give a complete classification of irreducible finite dimensional representations of the nonstandard q-deformation U'_q(so(n)) (which does not coincide with the Drinfeld-Jimbo quantum algebra U_q(so(n)) of the universal enveloping algebra U(so(n,C)) of the Lie algebra so(n,C) when q is not a root of unity. These representations are exhausted by irreducible representations of the classical type and of the nonclassical type. Theorem on complete reducibility of finite dimensional representations of U'_q(so(n)) is proved.

math.QA↗

arXiv2007

On factorization of q-difference equation for continuous q-Hermite polynomials

We argue that a customary q-difference equation for the continuous q-Hermite polynomials H_n(x|q) can be written in the factorized form as (D_q^2 - 1)H_n(x|q)=(q^{-n}-1)H_n(x|q), where D_q is some explicitly known q-difference operator. This means that the polynomials H_n(x|q) are in fact governed by the q-difference equation D_qH_n(x|q)=q^{-n/2}H_n(x|q), which is simpler than the conventional one.

math.CA↗

arXiv2005

Duality of q-polynomials, orthogonal on countable sets of points

We review properties of q-orthogonal polynomials, related to their orthogonality, duality and connection with the theory of symmetric (self-adjoint) operators, represented by a Jacobi matrix. In particular, we show how one can naturally interpret the duality of families of q-polynomials, orthogonal on countable sets of points. In order to obtain orthogonality relations for dual sets of polynomials, it is proposed to use two symmetric (self-adjoint) operators, representable (in some distinct bases) by Jacobi matrices. This approach is applied to several pairs of dual families of q-polynomials, orthogonal on countable sets, from the q-Askey scheme. For each such pair, the corresponding operators, representable by Jacobi matrices, are explicitly given. These operators are employed in order to find explicitly sets, on which the polynomials are orthogonal, and orthogonality relations for them.

math.CA↗

arXiv2004

On discrete q-ultraspherical polynomials and their duals

We show that a confluent case of the big q-Jacobi polynomials P_n(x;a,b,c;q), which corresponds to a=b=-c, leads to a discrete orthogonality relation for imaginary values of the parameter a (outside of its commonly known domain 0 1, this family represents yet another q-extension of these classical polynomials, different from the continuous q-ultraspherical polynomials of Rogers. The dual family with respect to the polynomials P_n(x;a,a,-a;q) (i.e., the dual discrete q-ultraspherical polynomials) corresponds to the indeterminate moment problem, that is, these polynomials have infinitely many orthogonality relations. We find orthogonality relations for these polynomials, which have not been considered before. In particular, extremal orthogonality measures for these polynomials are derived.

math.CA↗

arXiv2003

A set of orthogonal polynomials, dual to alternative q-Charlier polynomials

The aim of this paper is to derive (by using two operators, representable by a Jacobi matrix) a family of q-orthogonal polynomials, which turn to be dual to alternative q-Charlier polynomials. A discrete orthogonality relation and a three-term recurrence relation for these dual polynomials are explicitly obtained. The completeness property of dual alternative q-Charlier polynomials is also established.

math.CA↗

arXiv2003

On q-orthogonal polynomials, dual to little and big q-Jacobi polynomials

This paper studies properties of q-Jacobi polynomials and their duals by means of operators of the discrete series representations for the quantum algebra U_q(su_{1,1}). Spectrum and eigenfunctions of these operators are found explicitly. These eigenfunctions, when normalized, form an orthogonal basis in the representation space. The initial U_q(su_{1,1})-basis and the bases of these eigenfunctions are interconnected by matrices, whose entries are expressed in terms of little and big q-Jacobi polynomials. The orthogonality by rows in these unitary connection matrices leads to the orthogonality relations for little and big q-Jacobi polynomials. The orthogonality by columns in the connection matrices leads to an explicit form of orthogonality relations on the countable set of points for {}_3ϕ_2 and {}_3ϕ_1 polynomials, which are dual to big and little q-Jacobi polynomials, respectively. The orthogonality measure for the dual little q-Jacobi polynomials proves to be extremal, whereas the measure for the dual big q-Jacobi polynomials is not extremal.

math.CA↗

arXiv2003

Big q-Laguerre and q-Meixner polynomials and representations of the algebra U_q(su(1,1))

Diagonalization of a certain operator in irreducible representations of the positive discrete series of the quantum algebra U_q(su(1,1)) is studied. Spectrum and eigenfunctions of this operator are found in an explicit form. These eigenfunctions, when normalized, constitute an orthonormal basis in the representation space. The initial U_q(su(1,1))-basis and the basis of eigenfunctions are interrelated by a matrix with entries, expressed in terms of big q-Laguerre polynomials. The unitarity of this connection matrix leads to an orthogonal system of functions, which are dual with respect to big q-Laguerre polynomials. This system of functions consists of two separate sets of functions, which can be expressed in terms of q-Meixner polynomials M_n(x;b,c;q) either with positive or negative values of the parameter b. The orthogonality property of these two sets of functions follows directly from the unitarity of the connection matrix. As a consequence, one obtains an orthogonality relation for q-Meixner polynomials M_n(x;b,c;q) with b<0. A biorthogonal system of functions (with respect to the scalar product in the representation space) is also derived.

math.QA↗

arXiv2003

Hamiltonian Type Operators in Representations of the Quantum Algebra U_q(su_{1,1})

We study some classes of symmetric operators for the discrete series representations of the quantum algebra U_q(su_{1,1}), which may serve as Hamiltonians of various physical systems. The problem of diagonalization of these operators (eigenfunctions, spectra, overlap coefficients, etc.) is solved by expressing their overlap coefficients in terms of the known families of q-orthogonal polynomials. We consider both bounded and unbounded operators. In the latter case they are not selfadjoint and have deficiency indices (1,1), which means that they have infinitely many selfadjoint extensions. We find possible sets of point spectrum (which depends on the representation space under consideration) for one of such symmetric operators by using the orthogonality relations for q-Laguerre polynomials. In another case we are led to new orthogonality relations for {}_3ϕ_1-hypergeometric polynomials. Many new realizations for the discrete series representations are constructed, which follows from the diagonalization of the operators considered. In particular, a new system of orthogonal functions on a discrete set is shown to emerge.

math.QA↗

arXiv2003

Harmonics on the Quantum Euclidean Space Related to the Quantum Orthogonal Group

The aim of this paper is to study harmonic polynomials on the quantum Euclidean space E^N_q generated by elements x_i, i=1,2,...,N, on which the quantum group SO_q(N) acts. The harmonic polynomials are defined as solutions of the equation Δ_q p=0, where p is a polynomial in x_i, i=1,2,...,N, and the q-Laplace operator Δ_q is determined in terms of the differential operators on E^N_q. The projector H_m: {cal A}_m\to {\cal H}_{m} is constructed, where {\cal A}_{m} and {\cal H}_m are the spaces of homogeneous of degree m polynomials and homogeneous harmonic polynomials, respectively. By using these projectors, a q-analogue of the classical zonal polynomials and associated spherical polynomials with respect to the quantum subgroup SO_q(N-2) are constructed. The associated spherical polynomials constitute an orthogonal basis of {\cal H}_m. These polynomials are represented as products of polynomials depending on q-radii and x_j, x_{j'}, j'=N-j+1. This representation is in fact a q-analogue of the classical separation of variables. The dual pair (U_q(sl_2), U_q(so_n)) is related to the action of SO_q(N) on E^N_q. Decomposition into irreducible constituents of the representation of the algebra U_q(sl_2)\times U_q(so_n) defined by the action of this algebra on the space of all polynomials on E^N_q is given.

math.QA↗

arXiv2002

A Laplace operator and harmonics on the quantum complex vector space

The aim of this paper is to study the q-Laplace operator and q-harmonic polynomials on the quantum complex vector space generated by z_i,w_i, i=1,2,...,n, on which the quantum group GL_q(n) (or U_q(n)) acts. The q-harmonic polynomials are defined as solutions of the equation Delta_qp=0, where p is a polynomial in z_i,w_i, i=1,2,...,n, and the q-Laplace operator Delta_q is determined in terms of q-derivatives. The q-Laplace operator Delta_q commutes with the action of GL_q(n). The projector H_{m,m'}: A_{m,m'} --> H_{m,m'} is constructed, where A_{m,m'} and H_{m,m'} are the spaces of homogeneous (of degree m in z_i and of degree m' in w_i) polynomials and homogeneous q-harmonic polynomials, respectively. By using these projectors, a q-analogue of the classical zonal spherical and associated spherical harmonics are constructed. They constitute an orthogonal basis of H_{m,m'}. A q-analogue of separation of variables is given. The quantum algebra U_q(gl_n), acting on H_{m,m'}, determines an irreducible representation of U_q(gl_n). This action is explicitly constructed. The results of the paper lead to the dual pair (U_q(sl_2), U_q(gl_n)) of quantum algebras.

math.QA↗

arXiv2002

q-Deformed Orthogonal and Pseudo-Orthogonal Algebras and Their Representations

Deformed orthogonal and pseudo-orthogonal Lie algebras are constructed which differ from deformations of Lie algebras in terms of Cartan subalgebra and root vectors and which make it possible to construct representations by operators acting according to Gel'fand--Tsetlin-type formulas. Unitary representations of the q-deformed algebras U_q(so_{n,1}) are found.

math.QA↗

arXiv2001

Classification of irreducible representations of the q-deformed algebra U'_q(so_n)

A classification of finite dimensional irreducible representations of the nonstandard $q$-deformation $U'_q(so_n)$ of the universal enveloping algebra $U(so(n, C))$ of the Lie algebra $so(n, C)$ (which does not coincides with the Drinfeld--Jimbo quantized universal enveloping algebra $U_q(so_n)$) is given for the case when $q$ is not a root of unity. It is shown that such representations are exhausted by representations of the classical and nonclassical types. Examples of the algebras $U'_q(so_3)$ and $U'_q(so_4)$ are considered in detail. The notions of weights, highest weights, highest weight vectors are introduced. Raising and lowering operators for irreducible finite dimensional representations of $U'_q(so_n)$ and explicit formulas for them are given. They depend on a weight upon which they act. Sketch of proofs of the main assertions are given.

math.QA↗

arXiv2001

Representations of the q-deformed algebra U'_q(so_4)

We study the nonstandard $q$-deformation $U'_q({\rm so}_4)$ of the universal enveloping algebra $U({\rm so}_4)$ obtained by deforming the defining relations for skew-symmetric generators of $U({\rm so}_4)$. This algebra is used in quantum gravity and algebraic topology. We construct a homomorphism $ϕ$ of $U'_q({\rm so}_4)$ to the certain nontrivial extension of the Drinfeld--Jimbo quantum algebra $U_q({\rm sl}_2)^{\otimes 2}$ and show that this homomorphism is an isomorphism. By using this homomorphism we construct irreducible finite dimensional representations of the classical type and of the nonclassical type for the algebra $U'_q({\rm so}_4)$. It is proved that for $q$ not a root of unity each irreducible finite dimensional representation of $U'_q({\rm so}_4)$ is equivalent to one of these representations. We prove that every finite dimensional representation of $U'_q({\rm so}_4)$ for $q$ not a root of unity is completely reducible. It is shown how to construct (by using the homomorphism $ϕ$) tensor products of irreducible representations of $U'_q({\rm so}_4)$. (Note that no Hopf algebra structure is known for $U'_q({\rm so}_4)$.) These tensor products are decomposed into irreducible constituents.

math.QA↗

arXiv2000

The Nonstandard Deformation U'_q(so_n) For q a Root of Unity

We describe properties of the nonstandard q-deformation U'_q(so_n) of the universal enveloping algebra U(so_n) of the Lie algebra so_n which does not coincide with the Drinfeld--Jimbo quantum algebra U_q(so_n). In particular, it is shown that there exists an isomorphism from U'_q(so_n) to U_q(sl_n) and that finite dimensional irreducible representations of U'_q(so_n) separate elements of this algebra. Irreducible representations of the algebras U'_q(so_n) for q a root of unity q^p=1 are given. The main class of these representations act on p^N-dimensional linear space (where N is a number of positive roots of the Lie algebra so_n) and are given by r=dim so_n complex parameters. Some classes of degenerate irreducible representations are also described.

math.QA↗

arXiv1999

Nonclassical type representations of the q-deformed algebra $U'_q({\rm so}_n)$

The nonstandard q-deformation $U'_q({\rm so}_n)$ of the universal enveloping algebra $U({\rm so}_n)$ has irreducible finite dimensional representations which are a q-deformation of the well-known irreducible finite dimensional representations of $U({\rm so}_n)$. But $U'_q({\rm so}_n)$ also has irreducible finite dimensional representations which have no classical analogue. The aim of this paper is to give these representations which are called nonclassical type representations. They are given by explicit formulas for operators of the representations corresponding to the generators of $U'_q({\rm so}_n)$.

math.QA↗

arXiv1999

Nonstandard q-deformation of the universal enveloping algebra $U'({\rm so}_n)$

We describe properties of the nonstandard q-deformation $U'_q({\rm so}_n)$ of the universal enveloping algebra $U({\rm so}_n)$ of the Lie algebra ${\rm so}_n$ which does not coincide with the Drinfeld--Jimbo quantum algebra $U_q({\rm so}_n)$. Irreducible representations of this algebras for q a root of unity q^p=1 are given. These representations act on p^N-dimensional linear space (where N is a number of positive roots of the Lie algebra ${\rm so}_n$) and are given by $r={\rm dim} {\rm so}_n$ complex parameters.

math.QA↗

arXiv1999

Nonclassical representations of the nonstandard deformations U'_q(so_n), U_q(iso_n) and U'_q(so_{n,1})

The aim of this paper is to announce the results on irreducible nonclassical type representations of the nonstandard q-deformations U'_q(so_n), U_q(iso_n) and U'_q(so_{n,1}) of the universal enveloping algebras of the Lie algebras so(n,C), iso_n and so_{n,1} when q is a real number (the algebra U'_q(so_{n,1}) is a real form of the algebra U'_q(so_{n+1})). These representations are characterized by the properties that they are singular at the point q=1.

math.QA↗

arXiv1999

Representations of the q-deformed algebra $U_q({\rm iso}_2)$

An algebra homomorphism $ψ$ from the q-deformed algebra $U_q({\rm iso}_2)$ with generating elements $I$, $T_1$, $T_2$ and defining relations $[I,T_2]_q=T_1$, $[T_1,I]_q=T_2$, $[T_2,T_1]_q=0$ (where $[A,B]_q=q^{1/2}AB-q^{-1/2}BA$) to the extension ${\hat U}_q({\rm m}_2)$ of the Hopf algebra $U_q({\rm m}_2)$ is constructed. The algebra $U_q({\rm iso}_2)$ at $q=1$ leads to the Lie algebra ${\rm iso}_2 \sim {\rm m}_2$ of the group ISO(2) of motions of the Euclidean plane. The Hopf algebra $U_q({\rm m}_2)$ is treated as a Hopf $q$-deformation of the universal enveloping algebra of ${\rm iso}_2$ and is well-known in the literature. Not all irreducible representations of $U_q({\rm m}_2)$ can be extended to representations of the extension ${\hat U}_q({\rm m}_2)$. Composing the homomorphism $ψ$ with irreducible representations of ${\hat U}_q({\rm m}_2)$ we obtain representations of $U_q({\rm iso}_2)$. Not all of these representations of $U_q({\rm iso}_2)$ are irreducible. The reducible representations of $U_q({\rm iso}_2)$ are decomposed into irreducible components. In this way we obtain all irreducible representations of $U_q({\rm iso}_2)$ when $q$ is not a root of unity. A part of these representations turns into irreducible representations of the Lie algebra iso$_2$ when $q\to 1$. Representations of the other part have no classical analogue.

math.QA↗