78 results for Kalnins, Ernie G., Journal article

Lie theory and separation of variables. 3. The equation ftt−fss =γ2f
Kalnins, Ernie G.; Miller, W., Jr. (197407)
Journal article
University of WaikatoKalnins has related the 11 coordinate systems in which variables separate in the equation ftt−fss = γ 2f to 11 symmetric quadratic operators L in the enveloping algebra of the Lie algebra of the pseudoEuclidean group in the plane E(1,1). There are, up to equivalence, only 12 such operators and one of them, LE, is not associated with a separation of variables. Corresponding to each faithful unitary irreducible representation of E(1,1) we compute the spectral resolution and matrix elements in an L basis for seven cases of interest and also give overlap functions between different bases: Of the remaining five operators three are related to Mathieu functions and two are related to exponential solutions corresponding to Cartesian type coordinates. We then use these results to derive addition and expansion theorems for special solutions of ftt−fss = 2f obtained via separation of variables, e.g., products of Bessel, Macdonald and Bessel, Airy and parabolic cylinder functions. The exceptional operator LE is also treated in detail.
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Superintegrability and higher order integrals for quantum systems
Kalnins, Ernie G.; Kress, Jonathan M.; Miller, W., Jr. (2010)
Journal article
University of WaikatoWe refine a method for finding a canonical form of symmetry operators of arbitrary order for the Schrödinger eigenvalue equation HΨ ≡ (Δ2 + V)Ψ = EΨ on any 2D Riemannian manifold, real or complex, that admits a separation of variables in some orthogonal coordinate system. The flat space equations with potentials V = α(x + iy)k − 1/(x − iy)k + 1 in Cartesian coordinates, and V = αr² + β/r²cos ²kθ + γ/r²sin ²kθ (the Tremblay, Turbiner and Winternitz system) in polar coordinates, have each been shown to be classically superintegrable for all rational numbers k. We apply the canonical operator method to give a constructive proof that each of these systems is also quantum superintegrable for all rational k. We develop the classical analog of the quantum canonical form for a symmetry. It is clear that our methods will generalize to other Hamiltonian systems.
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Lie theory and separation of variables. 6. The equation iUt + ∆2U = 0
Boyer, C.P.; Kalnins, Ernie G.; Miller, W., Jr. (197503)
Journal article
University of WaikatoThis paper constitutes a detailed study of the nine−parameter symmetry group of the time−dependent free particle Schrödinger equation in two space dimensions. It is shown that this equation separates in exactly 26 coordinate systems and that each system corresponds to an orbit consisting of a commuting pair of first− and second−order symmetry operators. The study yields a unified treatment of the (attractive and repulsive) harmonic oscillator, linear potential and free particle Hamiltonians in a time−dependent formalism. Use of representation theory for the symmetry group permits simple derivations of addition and expansion theorems relating various solutions of the Schrödinger equation, many of which are new.
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Lie theory and separation of variables. 4. The groups SO (2,1) and SO (3)
Kalnins, Ernie G.; Miller, W., Jr. (197408)
Journal article
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University of Waikato 
The relativistically invariant expansion of a scalar function on imaginary Lobachevski space
Kalnins, Ernie G.; Miller, W., Jr. (197310)
Journal article
University of WaikatoUsing the previous analysis of Gel'fand and Graev a new relativistically invariant expansion of a scalar function on threedimensional imaginary Lobachevski space L3(I) is given. The coordinate system used corresponds to the horospherical reduction SO(3,1) E2 SO(2) and covers all of L3(I).
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Mixed basis matrix elements for the subgroup reductions of SO(2,1)
Kalnins, Ernie G. (197305)
Journal article
University of WaikatoBy using the irreducible decomposition on the twodimensional light cone, the mixed basis matrix elements for the three subgroup reductions of SO(2,1) are calculated. These matrix elements are calculated for the principal series only and can be expressed in terms of wellknown special functions. As a consequence of appearing in this context, some new properties of these special functions are given.
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Unitary Representations of the Homogeneous Lorentz Group in an O(1,1) O(2) Basis and Some Applications to Relativistic Equations
Kalnins, Ernie G. (197209)
Journal article
University of WaikatoUnitary irreducible representations of the homogeneous Lorentz group O(3, 1) belonging to the principal series are reduced with respect to the subgroup O(1,1) O(2). As an application we determine the mixed basis matrix elements between O(3) and O(1,1) O(2) bases and derive recurrence relations for them. This set of functions is then used to obtain invariant expansions of solutions of the Dirac and Proca free field equations. These expansions are shown to have the correct nonrelativistic limit.
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Lie theory and separation of variables. 11. The EPD equation
Kalnins, Ernie G. (197603)
Journal article
University of WaikatoWe show that the Euler–Poisson–Darboux equation {∂tt ∂rr – [(2m+1)/r]∂r}Ө=0 separates in exactly nine coordinate systems corresponding to nine orbits of symmetric secondorder operators in the enveloping algebra of SL(2,R), the symmetry group of this equation. We employ techniques developed in earlier papers from this series and use the representation theory of SL(2,R) to derive special function identities relating the separated solutions. We also show that the complex EPD equation separates in exactly five coordinate systems corresponding to five orbits of symmetric secondorder operators in the enveloping algebra of SL(2,C).
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Lie theory and separation of variables. 9. Orthogonal Rseparable coordinate systems for the wave equation ψtt∆2ψ=0
Kalnins, Ernie G.; Miller, W., Jr. (197603)
Journal article
University of WaikatoA list of orthogonal coordinate systems which permit Rseparation of the wave equation ψtt∆2ψ=0 is presented. All such coordinate systems whose coordinate curves are cyclides or their degenerate forms are given. In each case the coordinates and separation equations are computed. The two basis operators associated with each coordinate system are also presented as symmetric second order operators in the enveloping algebra of the conformal group O(3,2).
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Erratum: Lie theory and separation of variables. 3. The equation ftt − fss = γ2f
Kalnins, Ernie G.; Miller, W., Jr. (197507)
Journal article
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University of Waikato 
Lie theory and separation of variables. 7. The harmonic oscillator in elliptic coordinates and Ince polynomials
Boyer, C.P.; Kalnins, Ernie G.; Miller, W., Jr. (197503)
Journal article
University of WaikatoAs a continuation of Paper 6 we study the separable basis eigenfunctions and their relationships for the harmonic oscillator Hamiltonian in two space variables with special emphasis on products of Ince polynomials, the eigenfunctions obtained when one separates variables in elliptic coordinates. The overlaps connecting this basis to the polar and Cartesian coordinate bases are obtained by computing in a simpler Bargmann Hilbert space model of the problem. We also show that Ince polynomials are intimately connected with the representation theory of SU (2), the group responsible for the eigenvalue degeneracy of the oscillator Hamiltonian.
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Lie theory and separation of variables. 5. The equations iUt + Uxx = 0 and iUt + Uxx −c/x2 U = 0
Kalnins, Ernie G.; Miller, W., Jr. (197410)
Journal article
University of WaikatoA detailed study of the group of symmetries of the timedependent free particle Schrödinger equation in one space dimension is presented. An orbit analysis of all first order symmetries is seen to correspond in a welldefined manner to the separation of variables of this equation. The study gives a unified treatment of the harmonic oscillator (both attractive and repulsive), Stark effect, and free particle Hamiltonians in the time dependent formalism. The case of a potential c/x2 is also discussed in the time dependent formalism. Use of representation theory for the symmetry groups permits simple derivation of expansions relating various solutions of the Schrödinger equation, several of which are new.
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Lie theory and separation of variables. 10. Nonorthogonal Rseparable solutions of the wave equation ∂ttψ=∆2ψ
Kalnins, Ernie G.; Miller, W., Jr. (197603)
Journal article
University of WaikatoWe classify and discuss the possible nonorthogonal coordinate systems which lead to Rseparable solutions of the wave equation. Each system is associated with a pair of commuting operators in the symmetry algebra so(3,2) of this equation, one operator first order and the other second order. Several systems appear here for the first time.
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Lie theory and separation of variables. 8. Semisubgroup coordinates for Ψtt  ∆2Ψ = 0
Kalnins, Ernie G.; Miller, W., Jr. (197512)
Journal article
University of WaikatoWe classify and study all coordinate systems which permit Rseparation of variables for the wave equation in three space–time variables and such that at least one of the variables corresponds to a oneparameter symmetry group of the wave equation. We discuss 33 such systems and relate them to orbits of commuting operators in the enveloping algebra of the conformal group SO (3,2).
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Separation of variables and contractions on twodimensional hyperboloid
Kalnins, Ernie G.; Pogosyan, G.S.; Yakhno, Alexander (2012)
Journal article
University of WaikatoIn this paper analytic contractions have been established in the R → ∞ con traction limit for exactly solvable basis functions of the Helmholtz equation on the two dimensional twosheeted hyperboloid. As a consequence we present some new asymptotic formulae.
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Jacobi elliptic coordinates, functions of Heun and Lame type and the Niven transform
Kalnins, Ernie G.; Miller, W., Jr. (2005)
Journal article
University of WaikatoLame and Heun functions arise via separation of the Laplace equation in general Jacobi ellipsoidal or conical coordinates. In contrast to hypergeometric functions that also arise via variable separation in the Laplace equation, Lame and Heun functions have received relatively little attention, since they are rather intractable. Nonetheless functions of Heun type do have remarkable properties, as was pointed out in the classical book \Modern Analysis" by Whittaker and Watson who devoted an entire chapter to the subject. Unfortunately the beautiful identities appearing in this chapter have received little notice, probably because the methods of proof seemed obscure. In this paper we apply the modern operator characterization of variable separation and exploit the conformal symmetry of the Laplace equation to obtain product identities for Heun type functions. We interpret the Niven transform as an intertwining operator under the action of the conformal group. We give simple operator derivations of some of the basic formulas presented by Whittaker and Watson and then show how to generalize their results to more complicated situations and to higher dimensions.
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Separable coordinates for threedimensional complex riemannian spaces
Kalnins, Ernie G.; Miller, W., Jr. (1979)
Journal article
University of WaikatoIn this paper we study the problem of separation of variables for the equations: Helmholtz equation & HamiltonJacobi equation.
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Superintegrable systems in Darboux spaces
Kalnins, Ernie G.; Kress, Jonathan M.; Miller, W., Jr. (200312)
Journal article
University of WaikatoAlmost all research on superintegrable potentials concerns spaces of constant curvature. In this paper we find by exhaustive calculation, all superintegrable potentials in the four Darboux spaces of revolution that have at least two integrals of motion quadratic in the momenta, in addition to the Hamiltonian. These are twodimensional spaces of nonconstant curvature. It turns out that all of these potentials are equivalent to superintegrable potentials in complex Euclidean 2space or on the complex 2sphere, via "coupling constant metamorphosis" (or equivalently, via Stäckel multiplier transformations). We present a table of the results.
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Superintegrability in a nonconformallyflat space
Kalnins, Ernie G.; Kress, Jonathan M.; Miller, W., Jr. (2013)
Journal article
University of WaikatoSuperintegrable systems in two and threedimensional spaces of constant curvature have been extensively studied. From these, superintegrable systems in conformally flat spaces can be constructed by Stackel transform. In this paper a method developed to establish the superintegrability of the TremblayTurbinerWinternitz system in two dimensions is extended to higher dimensions and a superintegrable system on a nonconformallyflat fourdimensional space is found. In doing so, curvature corrections to the corresponding classical potential are found to be necessary. It is found that some subalgebras of the symmetry algebra close polynomially.
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Superintegrability and higherorder constants for classical and quantum systems
Kalnins, Ernie G.; Miller, W., Jr.; Pogosyan, G.S. (2011)
Journal article
University of WaikatoWe extend recent work by Tremblay, Turbiner, and Winternitz which analyzes an infinite family of solvable and integrable quantum systems in the plane, indexed by the positive parameter k. Key components of their analysis were to demonstrate that there are closed orbits in the corresponding classical system if k is rational, and for a number of examples there are generating quantum symmetries that are higher order differential operators than two. Indeed they conjectured that for a general class of potentials of this type, quantum constants of higher order should exist. We give credence to this conjecture by showing that for an even more general class of potentials in classicalmechanics, there are higherorder constants of the motion as polynomials in the momenta. Thus these systems are all superintegrable.
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