843 research outputs found
Fourier and Gegenbauer expansions for a fundamental solution of the Laplacian in the hyperboloid model of hyperbolic geometry
Due to the isotropy -dimensional hyperbolic space, there exist a
spherically symmetric fundamental solution for its corresponding
Laplace-Beltrami operator. On the -radius hyperboloid model of
-dimensional hyperbolic geometry with and , we compute
azimuthal Fourier expansions for a fundamental solution of Laplace's equation.
For , we compute a Gegenbauer polynomial expansion in geodesic polar
coordinates for a fundamental solution of Laplace's equation on this
negative-constant sectional curvature Riemannian manifold. In three-dimensions,
an addition theorem for the azimuthal Fourier coefficients of a fundamental
solution for Laplace's equation is obtained through comparison with its
corresponding Gegenbauer expansion.Comment: arXiv admin note: substantial text overlap with arXiv:1201.440
One-Step Recurrences for Stationary Random Fields on the Sphere
Recurrences for positive definite functions in terms of the space dimension
have been used in several fields of applications. Such recurrences typically
relate to properties of the system of special functions characterizing the
geometry of the underlying space. In the case of the sphere the (strict) positive definiteness of the zonal function
is determined by the signs of the coefficients in the
expansion of in terms of the Gegenbauer polynomials , with
. Recent results show that classical differentiation and
integration applied to have positive definiteness preserving properties in
this context. However, in these results the space dimension changes in steps of
two. This paper develops operators for zonal functions on the sphere which
preserve (strict) positive definiteness while moving up and down in the ladder
of dimensions by steps of one. These fractional operators are constructed to
act appropriately on the Gegenbauer polynomials
Radial Coordinates for Conformal Blocks
We develop the theory of conformal blocks in CFT_d expressing them as power
series with Gegenbauer polynomial coefficients. Such series have a clear
physical meaning when the conformal block is analyzed in radial quantization:
individual terms describe contributions of descendants of a given spin.
Convergence of these series can be optimized by a judicious choice of the
radial quantization origin. We argue that the best choice is to insert the
operators symmetrically. We analyze in detail the resulting "rho-series" and
show that it converges much more rapidly than for the commonly used variable z.
We discuss how these conformal block representations can be used in the
conformal bootstrap. In particular, we use them to derive analytically some
bootstrap bounds whose existence was previously found numerically.Comment: 27 pages, 9 figures; v2: misprints correcte
Fourier and Gegenbauer Expansions for a Fundamental Solution of Laplace's Equation in Hyperspherical Geometry
For a fundamental solution of Laplace's equation on the -radius
-dimensional hypersphere, we compute the azimuthal Fourier coefficients in
closed form in two and three dimensions. We also compute the Gegenbauer
polynomial expansion for a fundamental solution of Laplace's equation in
hyperspherical geometry in geodesic polar coordinates. From this expansion in
three-dimensions, we derive an addition theorem for the azimuthal Fourier
coefficients of a fundamental solution of Laplace's equation on the 3-sphere.
Applications of our expansions are given, namely closed-form solutions to
Poisson's equation with uniform density source distributions. The Newtonian
potential is obtained for the 2-disc on the 2-sphere and 3-ball and circular
curve segment on the 3-sphere. Applications are also given to the
superintegrable Kepler-Coulomb and isotropic oscillator potentials
Large Parameter Cases of the Gauss Hypergeometric Function
We consider the asymptotic behaviour of the Gauss hypergeometric function
when several of the parameters a, b, c are large. We indicate which cases are
of interest for orthogonal polynomials (Jacobi, but also Krawtchouk, Meixner,
etc.), which results are already available and which cases need more attention.
We also consider a few examples of 3F2-functions of unit argument, to explain
which difficulties arise in these cases, when standard integrals or
differential equations are not available.Comment: 21 pages, 4 figure
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